International forensic scientists have reached the site of the flight MH17 crash in east Ukraine after the government halted military operations.
Australian and Dutch police experts arrived in a convoy of Organization for Security and Co-operation in Europe (OSCE) monitors.
Fighting between government and rebel forces had prevented them getting there for nearly a week.
Australia believes that around 80 bodies remain at the crash site.
Explosions were reportedly heard near the site after their arrival.
A journalist for AFP news agency heard several "powerful" blasts and saw a plume of smoke less than 10km (six miles) from the crash site.
Russian aviation experts are also in Ukraine, hoping to visit the site.
The Malaysia Airlines plane crashed on 17 July in eastern Ukraine, with the deaths of all 298 people on board.
The rebels deny that they shot it down with a missile by mistake.
Officials in Russia, which has been accused by the US and others of supplying the rebels with advanced weaponry, suggest that Ukraine's own armed forces downed the jet - a charge rejected by Kiev.
Russia has come under increased pressure to end its support for the rebels despite having continually denied claims that it is arming and training them.
In other developments
- Ukraine's parliament backed the potential deployment of up to 950 Dutch and Australian "armed personnel" at the crash site
- The parliament also rejected the resignation of Prime Minister Arseniy Yatsenyuk after the recent collapse of his coalition
- A new round of EU sanctions was revealed on Thursday following similar action by the US. Billionaire tycoon Arkady Rotenberg, a former judo sparring partner of President Vladimir Putin, is among those affected by EU travel bans and asset freezes
- Separatist rebels are reportedly due to meet a Ukrainian delegation on Friday in Minsk, as Belarus hosts talks involving Ukraine, Russia and the OSCE
OSCE monitors on the ground said in a tweet that they had reached the crash site with the Dutch and Australian investigators after using a new access route.
Getting out of their cars, they stopped for a minute's silence in remembrance of those killed almost two weeks ago to the hour.
The Dutch justice ministry told AFP the Dutch-Australian team was so far only a "reconnaissance" mission but would hopefully pave the way for more experts to visit soon.
It remains unclear when larger teams of police and forensics will be deployed, despite getting backing from the Ukrainian parliament, says the BBC's Tom Burridge in Kiev.
The Netherlands lost 193 of its citizens in the crash while Australia lost 27 and Malaysia 43.
Speaking on a visit to Kiev, Australian Foreign Minister Julie Bishop said she had been told that 80 bodies could still be at the crash site.
"We are determined to access the site, so that we can collect the remains with some dignity and return them to the Netherlands where they can be identified," she said.
"And then the grieving families across the world who lost 298 people can have some closure."
Malaysian Prime Minister Najib Razak said on a visit to the Netherlands that a team of 68 Malaysian police officers had arrived in Kiev to help with the investigation.
Speaking at a news conference, he and his Dutch counterpart, Mark Rutte, said they were united in mourning.
The Dutch prime minister outlined their three shared priorities: to repatriate the rest of the passengers' remains from Ukraine, to establish the cause of the crash and to bring those responsible to justice.
The crash area appears to be still under the control of rebel fighters, an AP news agency journalist at the scene said.
A Russian delegation led by Oleg Storchevoy, deputy head of Russia's federal air transport agency Rosaviatsia, arrived in Kiev earlier.
"Russian experts intend to meet the head of the investigative commission... and hand over all the materials that the chairman of the commission had previously asked for," Rosaviatsia said in a statement.
"Today, the Russian representatives will also try to reach the crash area of the Boeing 777 and together with specialists from the international investigative commission examine the state of parts of the aircraft at the site."
There was no comment on the Russians' involvement from Ukrainian and Dutch officials approached by AP.
The press service for Ukraine's "anti-terrorist operation" said troops would refrain from combat operations in the Donetsk region, except in self-defence, in order to allow investigators to do their work on Thursday.
Well over 1,000 civilians and combatants have been killed since the new Ukrainian government sent troops into east Ukraine in mid-April to quell the insurgency.
The rebels have been forced back towards their strongholds in the cities of Donetsk and Luhansk, which have come under heavy bombardment.