The death toll in the Christchurch massacre has risen to 50 after a body was discovered at one of the mosques where a gunman opened fire on worshippers.

The latest victim was found as officials removed bodies from Al Noor mosque, where most of the victims were killed, said New Zealand police commissioner Mike Bush. The number of people injured has also risen to 50, he added.

Eleven of the wounded were in a critical condition, with two fighting for their lives, according to New Zealand Police.

The gunman Brenton Tarrant, is believed to have acted alone, Mr Bush said at a press conference on Sunday. Three other people were arrested following Friday's shooting, but two have since been released and the third charged with firearms offences which police said were not directly linked to the attacks.

New Zealand's prime minister, Jacinda Ardern, who laid flowers for victims and comforted worshippers at a mosque in Wellington on Sunday, has confirmed reports her office received "manifesto" by Tarrant minutes before the shooting.

New Zealand shootings: Victims of Christchurch mosque terror attacks Show all 11 1 /11 New Zealand shootings: Victims of Christchurch mosque terror attacks New Zealand shootings: Victims of Christchurch mosque terror attacks Zakaria Bhuiyan People gather hoping to find out information about Zakaria Bhuiyan who is still missing after the mosques shootings in Christchurch. David Moir/AFP New Zealand shootings: Victims of Christchurch mosque terror attacks Mucad Ibrahim Three-year-old Mucad Ibrahim, the youngest known victim of the mass shooting at two mosques in Christchurch, New Zealand, on 15 March 2019. Abdi Ibrahim via AP New Zealand shootings: Victims of Christchurch mosque terror attacks Nadeem Rasheed Nadeem Rasheed, brother of Pakistani Naeem Rashid who died alongside his son Talha Naeem, 21, who were killed in shooting at a Mosque in Christchurch, at their home town in Abbottabad, EPA New Zealand shootings: Victims of Christchurch mosque terror attacks Omar Nabi Omar Nabi speaks to the media about losing his father Haji Daoud Nabi, 71, in the mosque attack REUTERS New Zealand shootings: Victims of Christchurch mosque terror attacks Ash Mohammed Ash Mohammed, right, talks to a police officer about his father and two brothers who are missing near the Masjid Al Noor mosque AP New Zealand shootings: Victims of Christchurch mosque terror attacks Akhtar Khokhur Akhtar Khokhur, 58, shows a picture of her missing husband Mehaboobbhai Khokhar, 65. AP New Zealand shootings: Victims of Christchurch mosque terror attacks Wasseim Alsati A note is seen on a window of a door at the family home of Wasseim Alsati in Christchurch on 17 March 2019. AFP/Getty Images New Zealand shootings: Victims of Christchurch mosque terror attacks Haroon Mahmood Relatives offer condolences to nephew (centre) of Haroon Mahmood, a Pakistani citizen who was killed in Christchurch mosque shootings. AP New Zealand shootings: Victims of Christchurch mosque terror attacks Farid Ahmed Farid Ahmed (pictured) survived the Al Noor mosque shootings but his wife Husne was killed. AFP/Getty Images New Zealand shootings: Victims of Christchurch mosque terror attacks Syed Areeb Ahmed A relative shows a picture of Syed Areeb Ahmed, a Pakistani citizen who was killed the Christchurch mosque shooting. AP New Zealand shootings: Victims of Christchurch mosque terror attacks Naeem Rashid A relative looks at a picture on a mobile phone of Pakistani nationals Naeem Rashid and his son Talha Naeem (right) who died in the Christchurch shootings. AFP/Getty Images

The document, also sent to media outlets and 29 other parliamentary email addresses, was sent nine minutes before the attack began.

"It did not include a location, it did not include specific details,” Ms Ardern said. “I am advised that within two minutes of its receipt, at least my office it was conveyed directly to parliamentary security.”

The prime minister said she would hold a cabinet meeting to discuss tightening New Zealand's gun laws on Monday.

She added there were “questions to be answered” by technology companies about the role social media played in disseminating video of the Christchurch attack, which was live-streamed online by the shooter.

Ms Ardern confirmed she had been contacted by Sheryl Sandberg, Facebook’s chief operating officer, in the wake of the shootings.

Facebook said it had removed 1.5m videos of the shooting in the first 24 hours after the attack, with 1.2m of those blocked at upload.

Police confirmed on Sunday that two children were killed in the shooting.

A four-year-old girl was also reported to be among the seriously injured. She was named as Elin by her uncle Sabri Daraghmeh, who told reporters in a phone call from Jordan that she remained in "the danger phase".

Her 33-year-old father, Mr Daraghmeh's brother, is said to be in a stable condition. The Jordanian citizen of Palestinian origin is reported to have moved to New Zealand five years ago and described it as "the safest place one could ever live in".

Fourteen-year-old Sayyad Milne was also confirmed dead. “I haven’t heard officially yet that he’s actually passed, but I know he has because he was seen," said his father, John.

New Zealand Prime Minister Jacinda Ardern says gun laws will change

Greg Robertson, chief of surgery at Christchurch Hospital described the "horror" and "anger" of hospital staff as the scale of the massacre became apparent.

"This is not something that we expected to see in our environment," he said. "We do see gunshot wounds, but 40, 50 people in a day is more than we should see."

Describing the difficulty of "comprehending the incomprehensible", he added: "Most people cope with things pretty well when you're doing things. It's when you go home and you think about it that that's when the issues start to declare themselves."

Mr Robertson said the injured had begun arriving at the hospital in cars as well as ambulances following the shootings.

Mr Bush, who had earlier called the attack a very well-planned event, said the suspect was not known to police either in New Zealand or Australia.

He said victims' families would be supported by a very large contingent of ethnic liaison officers working with religious leaders and other support people. "There is so much outpouring of grief ... and we have to support those people and meet their needs," he said.

Later in the day, police said a search of the suspect's property in Dunedin had been completed. "A number of items of interest were located, however no items that would present harm to members of the public were discovered," police said.

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Tarrant, a 28-year-old Australian, appeared in court on Saturday charged with one count of murder. He was remanded until 5 April. Police said further charges would follow.

The terror attack on worshippers at Al Noor mosque in central Christchurch was live-streamed on Facebook. The gunman then travelled to nearby Linwood mosque, where he again opened fire.

In the video a man inside the Al Noor mosque said "Welcome, brother" as the gunman approaches and begins to shoot.

Mr Bush said it was obvious the gunman had modified a category A firearm, although he stressed the alleged shooter obtained a legitimate firearms licence in 2017 in New Zealand. The suspected attacker left behind a 74-page document in which he referred to anti-Islam and far-right conspiracy theories and white supremacist ideology.

Dressed in a white prison jumpsuit, he made a white power gesture at press cameras during an appearance at Christchurch District Court on Saturday morning, where he was charged with one count of murder.

Judge PR Kellar said it was reasonable to assume Mr Tarrant would face further murder charges, before remanding him in custody until he appears at New Zealand’s High Court on 5 April.

She said that some of the victims might have been new immigrants and refugees, who had chosen to make the country their home.

As the investigation into the attacks continues, it has emerged that people from Saudi Arabia, Pakistan, Malaysia, Indonesia, Turkey and Jordan were also among the dead.