The US first lady has tweeted her condolences to the families of victims.
Liverpool footballer Mohamed Salah sent his condolences to the victims of the shooting.
Theresa May says she has spoken with the New Zealand Prime Minister to "express the UK's deepest condolences at the horrifying terrorist attack."
She added: "To target Muslims as they were attending their place of worship is despicable."
- The minimum legal age to own a gun in New Zealand is 16 or 18 for military style semi-automatic weapons.
- Anyone over that age who is considered by police to be "fit and proper" can possess a firearm.
- All gun-owners must have a licence, but most individual weapons don't have to be registered.
Former US President Bill Clinton has responded to a tweet by New Zealand's Prime Minister Jacinda Ardern, saying that he "[mourns] all those murdered in Christchurch."
Mohammad Faisal, a spokesman for Pakistan's Ministry of Foreign Affairs, says four Pakistanis have been injured in the attack. Another five are unaccounted for.
The Christchurch shootings have reopened old wounds for Canada's Muslim community.
In 2017, Alexandre Bissonnette opened fire on worshippers at the Quebec Islamic Cultural Centre, killing six people and injuring five others.
Kais Chaouache, a member of the mosque, told Canadian broadcaster CBC: "Here, we belong to Quebec society, we are Quebeckers. In New Zealand, same thing. Why were they targeted by this act?"
Prime Minister Justin Trudeau noted the similarities between the two incidents in his message to the victims of the Christchurch attacks. He added: “To move forward as a world, we need to recognise diversity as a source of strength, and not a threat.”
As social media sites try to remove copies of the gunman's video, police - and members of the public - are urging others not to share or watch it.
New Zealand Police earlier advised: "Police are aware there is extremely distressing footage relating to the incident in Christchurch circulating online. We would strongly urge that the link not be shared. We are working to have any footage removed."
A family of Syrian refugees is among the victims of the Christchurch shootings, the group Syrian Solidarity New Zealand told the BBC.
Group member Ali Akil said the father was killed and his two sons were shot - one is in hospital, the other's whereabouts are unknown.
Their mother was not at the mosque at the time and heard her son being shot while he was on the phone to her during the attack, Mr Akil said.
Jewish Agency chair Isaac Herzog says that "for the first time" Jewish places of worship around New Zealand will be shut on Saturday - the Jewish sabbath.
One of the survivors of the attack has told Indian broadcaster NDTV that a man grabbed the gunman from behind, potentially saving their lives.
He said that he and friend saw the man "creep up behind the shooter and hold him until his gun dropped", before the gunman ran towards the door.
"If that hadn't happened, many more would have died and I wouldn't be here now," he added. The witness did not say in which mosque the incident happened.
Indian Prime Minister Narendra Modi has written to his New Zealand counterpart Jacinda Ardern condemning terrorism in all its forms, India's foreign ministry said.
Mr Modi expressed "deep shock and sadness", adding that: "Hatred and violence have no place in diverse and democratic societies."
Somalia's Ministry of Foreign Affairs has condemned the "brutal terrorist attack", saying it was "a heinous cowardly crime requiring a unified Islamic and international stand".
In a statement, it called on the government in New Zealand "to conduct a thorough investigation into this terrible terrorist act".
On Twitter, Somalia's President Mohamed Abdullahi Mohamed, also known as Farmajo, condemned the "horrific" attack.
Turkish foreign minister Mevlut Cavusoglu says media outlets and politicians who "promote Islamophobia" must also share responsibility for the deadly attack.
"It is not only the despicable people who committed this terrorist attack," he told reporters in Brussels.
"Political leaders and irresponsible media outlets that promote xenophobic and Islamophobic tendencies, and the use of hate speech against Muslims, also share - and I underline this - they also share responsibility."
Turkish President Recep Tayyip Erdogan also tweeted that the attack was "the latest example of rising racism and Islamophobia".
Buildings in Melbourne, Australia, have been lit up in red, white and blue - the colours of the New Zealand flag.
The Premier of Victoria, Daniel Andrews, tweeted that as well as lighting up the city's buildings, flags would be flown at half-mast.
An appeal to help survivors of the attacks has raised more than NZ$380,000 (£197,000) within hours of being set up.
It was launched by New Zealand charity Victim Support at about 21:40 on Friday local time and by 02:00 had about 6,000 donors.
The charity wrote: "All donations received through the fund will be ring-fenced to provide resources and support to those affected by this horrific incident. Victim Support stands with everyone affected and all communities in New Zealand today."
People have been leaving flowers and hand-written tributes at the door of Finsbury Park mosque in north-east London.
The mosque suffered its own attack in June 2017 when Darren Osborne deliberately drove a van into a crowd of worshippers.Copyright: PACopyright: PA
Former US presidential candidate Hillary Clinton said "we must continue to fight the perpetuation and normalisation of Islamophobia and racism in all its forms".
Former US president Barack Obama has tweeted his condolences to the people of New Zealand, and the global Muslim community.
The New Zealand Red Cross has published a list of missing persons on its website.
The missing have been listed as originating from countries including Somalia, Jordan, India, Pakistan, Bangladesh, Afghanistan and Saudi Arabia.
On Facebook, the Pakistan Association of New Zealand has posted names on of members who are missing.