A 28-year-old Australian man has been remanded in custody after a court appearance, with police saying more charges will be filed against him.
New Zealand has awoken grieving and on high alert after a massacre at two mosques in Christchurch left 49 dead and dozens more injured, as an Australian man appeared in court charged over the shootings.
Former NSW personal trainer Brenton Tarrant, 28, fronted a Christchurch court on Saturday on one count of murder, with police saying he is likely to face more charges.
Tarrant, who was reportedly wearing a tunic and was handcuffed, did not apply for bail or to have his name suppressed and has been remanded in custody without plea until April 5.
He did not speak, but was looking around particularly at the media present.
NZ Police closed the Christchurch court to the public over security concerns, but media was able to attend.
The unprecedented shootings, confirmed as an act of terror by Prime Minister Jacinda Ardern, has seen the country's threat level raised to high for the first time in its history.
Public events across the nation scheduled for the weekend have been cancelled amid safety fears, with police officers and helicopters on patrol.
"There is no guarantee the risk is limited to Canterbury and we need all New Zealanders to be extra vigilant," police said in the morning.
Officials say 41 people were killed at the Masjid Al Noor mosque on Deans Avenue, before shooting broke out at Linwood Masjid six kilometres away, leaving seven more dead. One other died in hospital.
Police on Saturday confirmed 42 were still being treated for injuries, including a five-year-old in critical condition.
Ardern vowed to change New Zealand's gun laws after confirming Tarrant had obtained a Category A gun licence in November 2017 and "under that, he was able to acquire the guns that he held".
The Australian gunman, who had based himself in Dunedin, used two semi-automatic weapons, two shotguns and a lever-action firearm, Ms Ardern said.
"When people, of course, hear that this individual had acquired a gun licence and acquired weapons of that range, then obviously I think people will be seeking change, and I'm committing to that," Ms Ardern told reporters in Wellington.
"There have been attempts to change our laws in 2005, 2012 and after an inquiry in 2017. Now is the time for change."
Reports of gunfire first came at about 1.40pm on Friday, armed officers descending on the Al Noor mosque near Hagley Oval, clearing the public from the area and sending the city into lockdown.
In signs police say show a well-planned attack, army personnel were also called in to dismantle explosive devices found in a stopped car and officers were in the evening searching a house in Dunedin, 360 kilometres away, clearing nearby homes for safety.
Witnesses described bloody scenes and bodies falling to the ground as worshippers ran for doors and the shooter moved from room to room for around 20 minutes.
One man, blood stains across his shirt, told AAP he hid under a bench and pretended to stop breathing as the gunman reloaded seven times.
"He went to all the different (rooms) and he shot everyone," he said.
Notification of a shooting at the second mosque followed, before video emerged of police ramming a car and pulling out the occupant.
None of those arrested had appeared on watchlist of New Zealand or Australian security agencies, police said.
Tarrant grew up in Grafton in NSW and stated in a rambling 74-page "manifesto" posted online before the attack he had spent years planning in vengeance for deaths in Europe, before deciding on Christchurch three months ago.
A post on a message board website linked to Tarrant also said the attack "against the invaders" would be live-streamed on social media.
A 17-minute video appeared online, taken from a helmet camera showed a shooter in his car, arming himself, getting out of the vehicle and entering the mosque where he started shooting. Authorities rushed to stop it circulating.
Earlier calling it one of the darkest days in her country's history, Ardern refused to accept it would change the character of a country that prides itself on peace, tolerance and has largely been untouched by global terror.
She is due to visit met with members of the Muslim community and first responders on Saturday.
Expression shock, sorrow and revulsion, Christchurch's mayor Lianne Dalziel called for her city to come together in kindness.
Leaders across the world, including Queen Elizabeth, British Prime Minister Theresa May, Pope Francis and United States president Donald Trump have sent condolences and condemned the attack.