Christchurch, Mar 16 (AFP): A right-wing extremist who filmed himself on a shooting rampage that left 49 mosque-goers dead flashed a white power gesture as he appeared in a New Zealand court on Saturday charged with murder.

Australian-born 28-year-old Brenton Tarrant stood in the dock wearing handcuffs and a white prison smock, as the judge read a single murder charge against him. A raft of further charges are expected.

The former fitness instructor and self-professed fascist occasionally turned to look at media present in court during the brief hearing that the public were excluded from for security reasons.

Flanked by armed police he made an upside-down "okay" signal, a symbol used by white power groups across the globe. He did not request bail and was taken into custody until his next court appearance which is scheduled for April 5.

A short distance from the court, 39 people were being treated in hospital for gunshot wounds and other injuries inflicted in the massacre.

The wounded included a two-year-old boy and a four-year-old girl, who was in critical condition.

Doctors at Christchurch hospital said they worked through the night in 12 operating theatres to treat the survivors.

The attack on the Al Noor and Linwood mosques has been labelled terrorism by Prime Minister Jacinda Ardern and is thought to be the deadliest attack directed against Muslims in the West in modern times.

Outside the court, the son of 71-year-old Afghan victim Daoud Nabi demanded justice for his late father, who believed New Zealand to be a "slice of paradise." "It's outrageous" he said. "It's beyond imagination." Ardern said the victims came from across the Muslim world, with Turkey, Bangladesh, Indonesia and Malaysia among the countries rendering consular assistance.

One Saudi citizen and two Jordanians were among the dead, while five Pakistani citizens were missing.

Ardern, wearing a black headscarf, met with survivors and victims' families Saturday at a college which has become an information centre for those affected by the tragedy.

Sahra Ahmed, a New Zealander of Somali origin, said she was touched by the PM's gesture.

"It means a lot. It is a signal to say -- I am with you," she told AFP.

The attack has prompted an outpouring of grief and deep shock in this usually peaceful and hospitable country, which prides itself on welcoming refugees fleeing violence or persecution.

The last comparable mass shooting in New Zealand was almost three decades ago, and the annual murder rate is usually around 50 people for the entire country.

Although shops were shuttered and many decided to stay at home Saturday, bouquets of flowers piled up at a makeshift memorial near the Al Noor mosque, many accompanied with handwritten letters laden with sadness and disbelief.

"I am so sorry that you were not safe here. Our hearts are breaking for your loss," read one of the notes marked with a string of x-kisses.

Ardern said the shooter was "in possession of a gun licence" obtained in November 2017, and he started legally purchasing the weapons the following month.

Two semi-automatic weapons, reportedly AR-15s, two shotguns and a lever-action gun were used in the attacks. Ardern said some of the guns had been modified to make them deadlier.

"I can tell you one thing right now -- our gun laws will change," she said.

The suspect documented his radicalisation and two years of preparations in a lengthy, meandering and conspiracy filled far-right "manifesto".

He live-streamed footage of himself going room-to-room, victim to victim, shooting the wounded from close range as they struggled to crawl away in the main Christchurch mosque.

Thirty-six minutes after the police received the first call, Tarrant was in custody.

Commissioner Mike Bush hailed the "absolute bravery" of both police and members of the public "who put themselves in harm's way" to apprehend the suspect.

"Their intervention may very likely have saved further lives." Some of the officers involved in the operation were rural police officers who Ardern said "put New Zealand first" Two other people remain in custody, although their link to the attack is not clear. One man, 18-year-old Daniel Burrough, has been charged with incitement.

Revulsion at the attack, and tributes to the victims, poured in from around the world, including from Pope Francis and Britain's Queen Elizabeth II.

US President Donald Trump condemned the "horrible massacre" in which "innocent people have so senselessly died", but denied that the problem of right-wing extremism was widespread.

Australian police said they had visited Tarrant's childhood home in the town of Grafton, north of Sydney, and spoken to family members as part of their investigation.

The attack has prompted searching questions about whether right-wing extremism has been treated with enough seriousness by Western governments.

Ali Soufan, a former high-ranking FBI counter-terrorism agent, warned the West was "in the midst of a surge of right-wing terrorism that has been metastasising in plain sight while generating only a muted response from domestic counter-terrorism authorities."

Ardern admitted "the individual charged with murder had not come to the attention of the intelligence community, nor the police, for extremism." "I have asked our agencies this morning to work swiftly on assessing whether there was any activity on social media or otherwise, that should have triggered a response." Ardern said these issues would be addressed at a cabinet meeting on Monday.