Accused Christchurch massacre gunman Brenton Harrison Tarrant made a white power gesture during a brief appearance in court.
Flanked by armed security officers, Tarrant smiled as he stood behind a small glass barrier which came up just above his eyes.
Tarrant, 28, from Australia, appeared to have live-streamed the terror attack in Christchurch and outlined his anti-immigrant motives in a manifesto posted online.
Prime Minister Jacinda Ardern said three people, including Tarrant, had been arrested in the wake of the attack.
A fourth person arrested on Friday who was in possession of a firearm, but with the intention of assisting police, has since been released.
Forty-one people were killed at the Masjid Al Noor mosque on Deans Avenue in central Christchurch, seven were killed at the suburban Linwood Masjid Mosque, and one person died at the Christchurch Hospital.
Ms Ardern said in a press conference that the country's gun laws would change in the wake of the attack.
The suspect held a Category A gun license which enabled him to legally obtain semi-automatic weapons, she said.
She added: "While the nation grapples with a form of grief and anger that we have not experienced before, we are seeking answers."
Prime Minister Ardern previously described the attack as "one of New Zealand's darkest days", adding: "What has happened here is an extraordinary and unprecedented act of violence."
She added: "It is clear that this can now only be described as a terrorist attack."
Police urged all mosques across New Zealand to stay closed over the weekend for security reasons.
British security sources said there were no apparent UK links to the attack.
Australian Prime Minister Scott Morrison earlier confirmed one of the people arrested was an Australian citizen, and described the suspected attacker as an "extremist right-wing violent terrorist".
In the video live-streamed by Tarrant, a man inside a mosque appears to say "Welcome brother" as a gunman approaches.
New Zealand Commissioner of Police Mike Bush said the attack was a "very well-planned event".
Asked if the police were searching for any other suspects, he said: "We never assume that there aren't other people involved, that's why we've got an immense presence out there ... but we don't have named or identified people that we are looking for, but it would be wrong to assume that there is no-one else."
He added: "At this point we are not actively looking for any identified persons."
A number of improvised explosive devices found on a vehicle after the shootings were defused by police.
Asked about the attackers not being on intelligence agency watchlists, Ms Ardern said it was an indication that they "had not acted in a way that warranted it".
Of the victims, she said: "I will have been amongst other members of the public who will have seen the footage as the injured were being brought to Christchurch A&E and you certainly can see from that footage there is a real range of ages there.
"I imagine that these would have represented particular brothers, fathers, sons."
She added: "We have undoubtedly experienced an attack today that is unprecedented, unlike anything that we have experienced before.
"But, as I say, New Zealand has been chosen because we are not a place where violent extremism exists.
"We reject those notions and we must continue to reject them. This is not an enclave for that kind of behaviour, for that kind of ideology.
"We will and must reject it. This is a place where people should feel secure and will feel secure.
"I am not going to let this change New Zealand's profile, none of us should."
In a message to the Governor-General of New Zealand, the Queen said: "I have been deeply saddened by the appalling events in Christchurch today. Prince Philip and I send our condolences to the families and friends of those who have lost their lives."
Officers responded to reports of shots fired in central Christchurch at about 1.40pm local time (12.40am GMT), and urged people in the area to stay indoors.
Members of the Bangladesh cricket team, currently on tour in New Zealand, said they had nearly been caught up in the tragedy.
Tamim Iqbal tweeted: "Entire team got saved from active shooters!!! Frightening experience and please keep us in your prayers", while Mushfiqur Rahim said: "Alhamdulillah Allah save us today while shooting in Christchurch in the mosque...we r extremely lucky...never want to see this things happen again.... pray for us".
New Zealand Police urged people not to share "extremely distressing footage" relating to the incident that was circulating online.
"It's very disturbing, it shouldn't be in the public domain," a spokesman said.
Meanwhile, leaders across the globe responded with outrage after Australian senator Fraser Anning apparently said in a statement shared online that the real cause of the attack was Muslim immigration.
The independent Queensland senator also tweeted: "Does anyone still dispute the link between Muslim immigration and violence?".
UK Home Secretary Sajid Javid accused him of fanning the flames of extremism, while Australian Prime Minister Scott Morrison called the views "disgusting".