Hundreds of mourners gathered in a Christchurch cemetery on Wednesday for the first funerals of those killed in last week's terror attack targeting two mosques as citizens braced for days of emotional farewells following the massacre.

The bodies of the victims were carried in open caskets on the shoulders of mourners into a large tent at Memorial Park Cemetery. Heavily armed police stood watch with flowers tucked in their revolver holsters and attached to their high powered rifles.

In a sign of lingering tensions, the PA system at the funeral announced evacuation procedures from the venue in the event of an emergency, mourners said.

Six victims were buried today, with more expected in the days to come. As of Tuesday night, just 21 victims had been identified, with the remainder expected to be completed on Wednesday before their bodies can be released for burial, police said. The victims' families have been frustrated by the delay.

Police Commissioner Mike Bush at a media briefing in the capital Wellington today explained the reasons behind the delay, saying that the police had to prove the cause of death to the satisfaction of the coroner and judge handling the case.

"You cannot convict for murder without that cause of death. So this is a very comprehensive process that must be completed to the highest standard," he said.

Twenty nine people wounded in the attacks remain in the hospital, with eight still in intensive care. Many have had to undergo multiple surgeries due to complicated gunshot wounds. The gunman used semi-automatic AR-15 rifles, with large magazines, and a shotgun.

The majority of victims were migrants or refugees from countries such as Pakistan, India, Malaysia, Indonesia, Turkey, Somalia, Afghanistan and Bangladesh. The youngest was a boy of three, born in New Zealand to Somali refugee parents.

The first two victims buried today, father and son Khalid and Hamza Mustafa, came from war-torn Syria. Khalid leaves behind a wife, daughter and son Zaid, 13, who was wounded in the twin attacks. In a powerful scene, Zaid sat in a wheelchair, his hands held aloft as he prayed alongside rows of mourners.

Jamil El-Biza, who came from the Sydney area to attend the funerals, told AFP that Zaid said at the graves of his brother and father: "I shouldn't be standing in front of you. I should be lying beside you."

Also attending was Abdul Aziz, an Afghan refugee who confronted the gunman at Linwood Mosque. He was embraced by many mourners.

"I cannot tell you how gutting it is...a family came here for safety and they should have been safe here," said Prime Minister Jacinda Ardern, visiting the city for the second time since the massacre.

Ardern also announced that the azaan for congregational prayers this coming Friday would be broadcast nationally followed by two minutes of silence for the 50 Muslims killed by Australian white supremacist Brenton Tarrant.

"There is a desire to show support for the Muslim community as they return to mosques on Friday," she said.

The bullet-ridden Al Noor mosque, where more than 40 people died, is being repaired for Friday prayers. The Australian National Imams Council has called on Imams to dedicate this Friday's Khutbah (sermon) to the victims of the attack.

"The attack on any Muslim or any innocent person anywhere around the world is an attack on all Muslims and all people," the council said in a statement.

"This is a human and an international tragedy, not only a Muslim and NZ tragedy. These acts of terror are there to divide us...and we reject this in all its forms and ways, but rather we will stay united and strong."

Muslims make up just 1 per cent of the total population of New Zealand, according to the country's last census which was carried out in 2013. The number of people identifying as Muslims rose by 28pc between 2006 and 2013, according to Stats NZ, with just over a quarter of them born in the country.

Many in the New Zealand Muslim community are converts from other religions and from local or European ethnic backgrounds.

Prime Minister Ardern, who sought to reassure the country's Muslims after the attack, received global praise for her outreach to the community in the days after the massacre, which she has termed terrorism.

Wearing a black scarf over her head, she was photographed hugging members of the Muslim community at a Christchurch refugee centre. She also vowed to change the country's gun laws, saying a ban on semi-automatic weapons would be considered.

On Tuesday, the 38-year-old leader had opened her remarks in parliament with a symbolic gesture, repeating the greeting uttered every day across the Islamic world: "As-Salaam Alaikum".

She has also announced an inquiry into the intelligence and security services' failures to detect the risk from the attacker or his plans.

Haka tribute paid to victims

Members of rival New Zealand gangs gathered in unity to slap their thighs, thump their chests and stick out their tongues in a traditional Maori haka to commemorate the victims of the terror attack.

Haka have reverberated not just around Christchurch, the largest city in New Zealand's South Island, but across the country and around the world, as New Zealand's multi-cultural diaspora attempts to honour the dead and stay connected with their homeland.

Usually adversaries, members of the Mongrel Mob, Black Power and Bandidos street gangs performed the haka outside Al Noor mosque.

"We came here out of respect for the fallen, and that's why we did the haka, its a sign of respect," Hamish Hiroki, national president of the Bandidos motorcycle gang, told Reuters.

"It was a Ngai Tahu haka because that's the tribe around here. It's used for pretty much all occasions."

Students at New Zealand's largest Muslim school in Auckland also performed the 'Ka Mate' haka, made famous by the All Blacks rugby team, in a demonstration of the place and importance of Maori culture in the country.

While the All Blacks have brought worldwide attention to haka, it has been misconstrued as a "war dance" or challenge because it is traditionally performed before matches.

In Maori culture, however, it means to simply dance or perform, and different haka are composed by different tribes for various uses and occasions. Haka expert Te Kahuata Maxwell said those being performed over the past week were a response to the trauma the community felt.

"It's the Maori way of dealing with death, it's the Maori way of expressing grief, it's the Maori way of expressing love. Haka is the Maori way of showing support, haka is part of Maori mourning," Maxwell, who is an associate professor at the University of Waikato, told Maori Television on Tuesday.

The 'Ka Mate' haka, which is the world's most recognisable, was composed by Ngati Toa chief Te Rauparaha in about 1820 as a celebration of life over death. It has been closely associated with New Zealand rugby since the 1888 unofficial “Natives” team toured Britain.

The practice was adopted by sporting teams of all types and is often performed at funerals, weddings and other major events.

Ardern calls for 'united front' on social media

Ardern at a press conference in Christchurch also spoke of the need for the world to confront the dangers posed by social media, even as a man accused of sharing a video of the massacre was jailed today until his next court appearance in mid-April.

"There is an argument there to be made for us to take a united front on what is a global issue," Ardern said. "This is not just an issue for New Zealand, the fact that social media platforms have been used to spread violence (and) material that incites violence."

Philip Arps, 44, appeared in a Christchurch court today on two charges of distributing the killer's livestream video the attack in a violation of the country's objectionable publications law. Each charge carries a maximum sentence of 14 years in prison.

Arps, heavily tattooed and dressed in a T-shirt and sweatpants, hasn't entered a plea. He remained expressionless during the hearing, his hands clasped behind his back. Judge Stephen O'Driscoll denied him bail.

Charging documents accuse Arps of distributing the video on Saturday, one day after the massacre.

International investigation

Tarrant, who was charged with at least one count of murder following the attack, was remanded into policy custody without a plea and is due back in court on April 5, when police said he is likely to face more charges.

New Zealand's police chief said global intelligence agencies, including the US Federal Bureau of Investigation and those from Australia, Canada and Britain, are building up a profile of the alleged shooter.

"I can assure you this is an absolute international investigation," said Police Commissioner Bush.

New Zealand has no death penalty and the terrorist is expected to face a record prison sentence if found guilty of the massacre. If convicted, he could be sentenced to life imprisonment without parole, criminal lawyer Simon Cullen told AFP, adding that such a sentence would be "unprecedented" for New Zealand.

Newbold said it was possible that Tarrant could spend the rest of his life in "segregation" and at least the first 5-10 years in "effective" solitary confinement. "There's a lot (of people) in segs who would get at him as well... he would have to be in highly-segregated conditions," Newbold said.

"If he's convicted, he will be effectively in solitary for a long, long time... he will be locked up most of the time in his own cell."

New Zealand's only maximum-security facility is the recently upgraded Auckland Prison at Paremoremo, 25 minutes north of Auckland where the nine-square-metre concrete block cells have a bed, toilet and shower all visible to staff via cameras.

Tarrant is said to be under 24-hour surveillance with no access to newspapers, television or other media. Prison authorities would likely arrange a special regime combining regular exercise with seclusion, for safety reasons.

Authorities say Tarrant is being held in a "specialist security facility" outside of Christchurch until his next court appearance.