President Vladimir Putin said all causes, including terrorism, were being investigated
No-one has said they were behind the blast but local media released CCTV footage of a bearded man
Foreign leaders have condemned the incident, with US President Donald Trump describing it as a "terrible thing".
We are ending our rolling coverage on this live page but you can continue to follow the latest developments
via our news story
and here is
everything we know
about Monday's events.
Putin: Thank you to drivers
Russian President Vladimir Putin has thanked St Petersburg's drivers for taking people home while metro services are suspended.
He said many motorists and taxi drivers were offering to carry passengers for free.
Hundreds of thousands of people in the city are travelling by foot, car, tram or bus while the metro system is closed, Mr Putin added.
AFP/GettyCopyright: AFP/Getty
Trump: St Petersburg explosion a 'terrible thing'
US President Donald Trump kept his thoughts on events in St Petersburg brief during an event at the White House.
Quote Message:
Happening all over the world, absolutely a terrible thing."
Happening all over the world, absolutely a terrible thing."
ReutersCopyright: Reuters
St Petersburg attack: What we know
We've been bringing you quick updates as new information comes out about the St Petersburg explosion, and have now compiled a round-up of what we know
here
.
American UN ambassador: We stand with you against extremists
The US ambassador to the UN has said her country stands with Russia against "extremist groups", despite authorities keeping an open mind about the cause of the explosion.
Nikki Haley shared a message of support for the people of St Petersburg, after up to 10 were killed on Monday.
Russia's Investigative Committee, a state body which investigates
major crimes, earlier said it was treating the explosion as a suspected "terrorist attack" - but was not ruling out other possibilities.
"Despite the fact that a criminal case under article 205 of the Criminal Code (act of terror) has been opened, the investigation intends on verifying all other possible versions of this incident," the committee said in a statement.
It has not pointed to possible perpetrators.
Anti-terror measures 'failed'
Senator Viktor Ozerov, who heads the Russian defence committee, said that anti-terror measures appeared to have failed on Monday.
"The tragedy in St Petersburg tells us that, somewhere, the anti-terror measures that have been taken... have not worked," Mr Ozerov said.
Speaking at the Russian parliament, he called for an investigation into the security measures in place on the St Petersburg metro system.
"Now we need to uncover the reasons why our system failed, and work out a series of measures so as not to allow such mistakes to be repeated."
His statement was broadcast live on the state-run news channel Rossiya 24.
Getty ImagesCopyright: Getty Images
People react to news of the deadly explosion at the Tekhnologichesky Institut metro station in St Petersburg
Image caption:
People react to news of the deadly explosion at the Tekhnologichesky Institut metro station in St Petersburg
Tributes appear for victims of St Petersburg explosion
ReutersCopyright: Reuters
A candle burns among the flowers left in tribute to victims of Monday's metro blast outside the Russian embassy in Minsk, Belarus
Image caption:
A candle burns among the flowers left in tribute to victims of Monday's metro blast outside the Russian embassy in Minsk, Belarus
ReutersCopyright: Reuters
At least 10 people were killed in the explosion. Pictured: Tributes outside the Kremlin in Moscow
Image caption:
At least 10 people were killed in the explosion. Pictured: Tributes outside the Kremlin in Moscow
AFPCopyright: AFP
People light candles for the victims outside Sennaya Ploshchad metro station
Image caption:
People light candles for the victims outside Sennaya Ploshchad metro station
Witness: 'There was no light and there was blood'
A woman travelling in the carriage next to the blast has described the moment the explosion ripped through the train to local media.
The woman, named only as Polina, told Bumaga (
in Russian
) it was standing room only as the metro moved between Sennaya Ploshchad and Tekhnologichesky Institut.
Quote Message:
There was a deafening bang, then a strong smell and smoke. People were pressed against each other. Two women immediately felt unwell and fell unconscious. Everything happened on the move, the train didn't stop."
There was a deafening bang, then a strong smell and smoke. People were pressed against each other. Two women immediately felt unwell and fell unconscious. Everything happened on the move, the train didn't stop."
When the train finally pulled into the station, she said they "saw that the neighbouring carriage was mangled, window glass was broken, there was no light and there was blood".
Quote Message:
People were being moved out of it. Some were being carried out, others supported."
People were being moved out of it. Some were being carried out, others supported."
Investigators 'will focus on two possible suspects'
Frank Gardner
BBC Security Correspondent
Quote Message:
The Russian authorities are sensibly being cautious before apportioning blame for Monday's metro blast. An earlier quote by the prosecutor-general that it was an act of terror was quickly retracted.
The Russian authorities are sensibly being cautious before apportioning blame for Monday's metro blast. An earlier quote by the prosecutor-general that it was an act of terror was quickly retracted.
Quote Message:
The FSB Security Service, the successors to the Soviet-era KGB, have skilled investigators, including forensic explosive experts. They will have been examining the explosive residue for clues, as well as the second device that was found intact. Their suspicions are likely to focus on two possible suspects, none yet confirmed.
The FSB Security Service, the successors to the Soviet-era KGB, have skilled investigators, including forensic explosive experts. They will have been examining the explosive residue for clues, as well as the second device that was found intact. Their suspicions are likely to focus on two possible suspects, none yet confirmed.
Quote Message:
One: An ISIS-inspired group enraged by recent Russian airstrikes in Syria. Two: Chechen nationalists (or even a combination of both).
One: An ISIS-inspired group enraged by recent Russian airstrikes in Syria. Two: Chechen nationalists (or even a combination of both).
Quote Message:
Both Chechen militants and international jihadists do have a track record of plotting to attack Russia's transport hubs, notably in Moscow. An estimated 7,000 Russians have travelled to Syria to join extremist groups and some have returned."
Both Chechen militants and international jihadists do have a track record of plotting to attack Russia's transport hubs, notably in Moscow. An estimated 7,000 Russians have travelled to Syria to join extremist groups and some have returned."
Metro driver praised by officials
The metro driver made the right decision not to stop his train before reaching the station, Russia’s Investigative Committee has said.
In a statement released on their website, the federal investigating authority said his actions may have prevented further victims and allowed for the swift evacuation of the injured.
The blast took place in the tunnel between two stations in central St Petersburg.
Security response 'will be uncompromising'
Oliver Carroll, the managing editor of the Moscow Times newspaper, has been speaking to BBC World News television.
He said that people in St Petersburg are not used to dealing with such attacks.
There have been attacks in Moscow in recent years, but the last major one was in 2010. In fact, Russia's main cities have been "remarkably terror-free" in the last few years, he says.
Mr Carroll says the security services have been "fairly uncompromising" in the troubled North Caucasus region, which is mainly Muslim, as well as taking "bold action" in Syria.
"So there is the grounds for an Islamic kind of terrorism," he said. "At the same time, there will be various conspiracy theories about the state themselves being behind it."
He cautions, however, that he does not want to give "too much weight" to such theories.
What is without doubt is that the government's response "will be uncompromising".
BBCCopyright: BBC
Russian PM calls St Petersburg blast a 'terrorist attack'
BBC Monitoring
Russian Prime Minister Dmitry Medvedev has written on Facebook:
Quote Message:
All those who were injured in the terrorist attack in St Petersburg metro will receive all the medical help they need. All instructions have been issued to the health and emergencies ministries. My most heartfelt commiserations go out to the friends and relatives of the victims of the explosion. This is our common pain.”
All those who were injured in the terrorist attack in St Petersburg metro will receive all the medical help they need. All instructions have been issued to the health and emergencies ministries. My most heartfelt commiserations go out to the friends and relatives of the victims of the explosion. This is our common pain.”
While Mr Medvedev calls it a terrorist attack, some Russian officials have been careful to not label it as such until their investigations are complete.
CCTV images of 'attacker' circulating on social media
CCTV images of the man suspected to be responsible for the St Petersburg explosion are circulating on social media.
The images appear to show a bearded man wearing a hat.
Earlier the Interfax news agency reported that CCTV cameras had captured images of the suspect.
The BBC cannot confirm any of these reports, and Russian officials are still investigating the cause of the explosion.
Recent attacks on public transport in Russia
Russia has a history of attacks on public transport.
In 2013,
two bomb blasts in two days
in the south-western city of Volgograd left more than 30 people dead and 62 needing hospital treatment.
The suicide bombings struck at the railway station on 29 December and on a bus on 30 December.
Volgograd's public transport system had already been targeted earlier in 2013. In October, a female suicide bomber
killed at least six people
when she detonated the explosives on a bus.
Before that, in 2009, a bomb exploded
on a high speed train
travelling between Moscow and St Petersburg, killing 27 and injuring another 130.
All attacks were claimed by Islamist groups.
Picture shows mangled doors of train
AFPCopyright: AFP
This picture shows the badly-damaged train, which came to a stop at the Tekhnologichesky Institut station in central St Petersburg
Image caption:
This picture shows the badly-damaged train, which came to a stop at the Tekhnologichesky Institut station in central St Petersburg
The situation in St Petersburg: What we know
BBCCopyright: BBC
An explosion has hit a train between two underground stations in St Petersburg
Officials say the cause of the blast, between Sennaya Ploshchad and Tekhnologichesky Institut stations, is yet to be determined
A spokesman for St Petersburg's governor says at least 10 people have been killed and 50 injured. But the Russian National Anti-Terrorist Committee says the death toll is nine, with 20 hurt
The committee said an explosive device was later found and made safe at another station, Ploshchad Vosstaniya
President Vladimir Putin says all causes, including terrorism, are being investigated
#Domoi: Locals use social media to help each other get home safely
This is reminiscent of the London and Paris attacks – the
hashtag
#домой
(#Domoi) is a big thing now.
On VKontakte, a social media network popular among Russians, and now also Twitter.
It means ‘Home’ – and ordinary people are using it to help others get home.
Here are two examples from VKontakte:
"Around 6pm. We’re able to take three people to the coastal
district. We’re going by the toll road. FREE. #Domoi."
"Guys! I have to get home to Muzhestva Ploshchad. Can anyone get me at least some of the way?
#Domoi."
'A horrific thing' - US man describes his experience
Rick Macy, 52, from
Massachusetts, works in St Petersburg and was in a metro car three stops
away. He heard the driver and dispatcher talking about the incident and he got
off the train.
Quote Message:
What a horrific thing. You could tell there was something happening, the dispatcher had a strained voice. When I heard that, I got off the train and came off the metro. It was horrible."
What a horrific thing. You could tell there was something happening, the dispatcher had a strained voice. When I heard that, I got off the train and came off the metro. It was horrible."
Quote Message:
Out on the streets, where I can see from our apartment, [there are] lots of people trying to get home. We are right by the Petrogradskaya, close to the station where the bomb went off. I am grateful that we are safe. We are going to stay home tonight."
Out on the streets, where I can see from our apartment, [there are] lots of people trying to get home. We are right by the Petrogradskaya, close to the station where the bomb went off. I am grateful that we are safe. We are going to stay home tonight."
In pictures: St Petersburg metro explosion
AFPCopyright: AFP
The explosion has killed at least nine people, officials say. Fifty others have been injured
Image caption:
The explosion has killed at least nine people, officials say. Fifty others have been injured
ReutersCopyright: Reuters
The explosion hit a carriage between two stations in central St Petersburg
Image caption:
The explosion hit a carriage between two stations in central St Petersburg
ReutersCopyright: Reuters
Officials say the cause of the explosion has yet to be determined
Image caption:
Officials say the cause of the explosion has yet to be determined
Breaking'Homemade device' disabled at different location
BBC Monitoring
News from around the globe
Russia's National Anti-Terrorist
Committee says a home-made explosive device has been disabled at Ploshchad Vosstaniya metro station in central St Petersburg.
It said an "improvised explosive
device has been discovered and disabled in a timely manner”.
The station is located about two miles away from the Tekhnologichesky Institut station.
Live Reporting
By Flora Drury and Kate Palmer
All times stated are UK
End of our live coverage
As the evening draws on in St Petersburg, locals are paying tributes to those killed and injured on Monday's attack.
The cause of the explosion has yet to be confirmed. Here is a round-up of what we know:
We are ending our rolling coverage on this live page but you can continue to follow the latest developments via our news story and here is everything we know about Monday's events.
Putin: Thank you to drivers
Russian President Vladimir Putin has thanked St Petersburg's drivers for taking people home while metro services are suspended.
He said many motorists and taxi drivers were offering to carry passengers for free.
Hundreds of thousands of people in the city are travelling by foot, car, tram or bus while the metro system is closed, Mr Putin added.
Trump: St Petersburg explosion a 'terrible thing'
US President Donald Trump kept his thoughts on events in St Petersburg brief during an event at the White House.
St Petersburg attack: What we know
We've been bringing you quick updates as new information comes out about the St Petersburg explosion, and have now compiled a round-up of what we know here .
Pictures of the aftermath can be found here .
American UN ambassador: We stand with you against extremists
The US ambassador to the UN has said her country stands with Russia against "extremist groups", despite authorities keeping an open mind about the cause of the explosion.
Nikki Haley shared a message of support for the people of St Petersburg, after up to 10 were killed on Monday.
Russia's Investigative Committee, a state body which investigates major crimes, earlier said it was treating the explosion as a suspected "terrorist attack" - but was not ruling out other possibilities.
"Despite the fact that a criminal case under article 205 of the Criminal Code (act of terror) has been opened, the investigation intends on verifying all other possible versions of this incident," the committee said in a statement.
It has not pointed to possible perpetrators.
Anti-terror measures 'failed'
Senator Viktor Ozerov, who heads the Russian defence committee, said that anti-terror measures appeared to have failed on Monday.
"The tragedy in St Petersburg tells us that, somewhere, the anti-terror measures that have been taken... have not worked," Mr Ozerov said.
Speaking at the Russian parliament, he called for an investigation into the security measures in place on the St Petersburg metro system.
"Now we need to uncover the reasons why our system failed, and work out a series of measures so as not to allow such mistakes to be repeated."
His statement was broadcast live on the state-run news channel Rossiya 24.
Tributes appear for victims of St Petersburg explosion
Witness: 'There was no light and there was blood'
A woman travelling in the carriage next to the blast has described the moment the explosion ripped through the train to local media.
The woman, named only as Polina, told Bumaga ( in Russian ) it was standing room only as the metro moved between Sennaya Ploshchad and Tekhnologichesky Institut.
When the train finally pulled into the station, she said they "saw that the neighbouring carriage was mangled, window glass was broken, there was no light and there was blood".
Investigators 'will focus on two possible suspects'
Frank Gardner
BBC Security Correspondent
Metro driver praised by officials
The metro driver made the right decision not to stop his train before reaching the station, Russia’s Investigative Committee has said.
In a statement released on their website, the federal investigating authority said his actions may have prevented further victims and allowed for the swift evacuation of the injured.
The blast took place in the tunnel between two stations in central St Petersburg.
Security response 'will be uncompromising'
Oliver Carroll, the managing editor of the Moscow Times newspaper, has been speaking to BBC World News television.
He said that people in St Petersburg are not used to dealing with such attacks.
There have been attacks in Moscow in recent years, but the last major one was in 2010. In fact, Russia's main cities have been "remarkably terror-free" in the last few years, he says.
Mr Carroll says the security services have been "fairly uncompromising" in the troubled North Caucasus region, which is mainly Muslim, as well as taking "bold action" in Syria.
"So there is the grounds for an Islamic kind of terrorism," he said. "At the same time, there will be various conspiracy theories about the state themselves being behind it."
He cautions, however, that he does not want to give "too much weight" to such theories.
What is without doubt is that the government's response "will be uncompromising".
Russian PM calls St Petersburg blast a 'terrorist attack'
BBC Monitoring
Russian Prime Minister Dmitry Medvedev has written on Facebook:
While Mr Medvedev calls it a terrorist attack, some Russian officials have been careful to not label it as such until their investigations are complete.
CCTV images of 'attacker' circulating on social media
CCTV images of the man suspected to be responsible for the St Petersburg explosion are circulating on social media.
The images appear to show a bearded man wearing a hat.
Earlier the Interfax news agency reported that CCTV cameras had captured images of the suspect.
The BBC cannot confirm any of these reports, and Russian officials are still investigating the cause of the explosion.
Recent attacks on public transport in Russia
Russia has a history of attacks on public transport.
In 2013, two bomb blasts in two days in the south-western city of Volgograd left more than 30 people dead and 62 needing hospital treatment.
The suicide bombings struck at the railway station on 29 December and on a bus on 30 December.
Volgograd's public transport system had already been targeted earlier in 2013. In October, a female suicide bomber killed at least six people when she detonated the explosives on a bus.
Three years earlier, at least 38 people died in a double suicide bombing on the Moscow metro .
Before that, in 2009, a bomb exploded on a high speed train travelling between Moscow and St Petersburg, killing 27 and injuring another 130.
All attacks were claimed by Islamist groups.
Picture shows mangled doors of train
The situation in St Petersburg: What we know
#Domoi: Locals use social media to help each other get home safely
This is reminiscent of the London and Paris attacks – the hashtag #домой (#Domoi) is a big thing now.
On VKontakte, a social media network popular among Russians, and now also Twitter.
It means ‘Home’ – and ordinary people are using it to help others get home.
Here are two examples from VKontakte:
"Around 6pm. We’re able to take three people to the coastal district. We’re going by the toll road. FREE. #Domoi."
"Guys! I have to get home to Muzhestva Ploshchad. Can anyone get me at least some of the way? #Domoi."
'A horrific thing' - US man describes his experience
Rick Macy, 52, from Massachusetts, works in St Petersburg and was in a metro car three stops away. He heard the driver and dispatcher talking about the incident and he got off the train.
In pictures: St Petersburg metro explosion
Breaking'Homemade device' disabled at different location
BBC Monitoring
News from around the globe
Russia's National Anti-Terrorist Committee says a home-made explosive device has been disabled at Ploshchad Vosstaniya metro station in central St Petersburg.
It said an "improvised explosive device has been discovered and disabled in a timely manner”.
The station is located about two miles away from the Tekhnologichesky Institut station.