Fifty people have died in the Christchurch mosque shooting, the worst terror attack in New Zealand history.
Here's what you need to know.
There were two attacks on Friday in Christchurch - one at the Masjid Al Noor Mosque next to Hagley Park, and one at the Linwood Mosque.
Fifty people have died, seven at Linwood Mosque and 42 at Masjid Al Noor Mosque. One person later died in Christchurch hospital.
The dead include a five-year-old girl and her father, who were chased by the gunman and shot in front of horrified passersby.
Fifty people were also injured, 36 remain in hospital with two in a critical condition. One child remains at Starship hospital.
The national security threat level has been increased from low to high for the first time in New Zealand's history.
What are the authorities saying?
Police believe the shootings at two mosques were the actions of a lone gunman.
Brenton Tarrant, 28, has been charged with murder, and more charges are likely. He has been remanded in custody until 5 April when he will appear in the high court.
Police said they don't believe the three other people arrested in Christchurch in the past two days were involved in the attacks.
Church services today
Security fears have led to the postponement of a large outdoor church service in Christchurch this morning.
Dean of Christchurch's Anglican Church, Lawrence Kimberley said he had hoped to hold a multi-denominational gathering on Sunday morning to show that Christians across the city stand in solidarity with the Muslim community.
But he said the church had followed police advice to postpone the service.
A mass of prayer for peace is to be held at St Mary's Catholic Pro Cathedral in Manchester Street.
Other churches are holding special prayer services. And some churches, including St Paul's Trinity Pacific Presbyterian church, have cancelled Sunday school as children are expected to be traumatised.
What the mayor of Christchurch said
Christchurch mayor Lianne Dalziel is encouraging residents to lay floral tributes along the Botanic Gardens wall.
She said people should stay away from the cordons near the city's two mosques, and instead take their flowers to a site in Rolleston Avenue.
Council staff are working today to prepare grave sites so that victims could be buried as soon as possible in line with the requirements and sensitivities of the Islamic religion, Ms Dalziel said.
Ms Dalziel said the Christchurch Foundation, which had been set up in the aftermath of the earthquakes, would make an announcement today about a fund to help with rebuilding communities and rebuilding what had been lost.
Vigils around the country
Vigils have been held around the country in support of the Muslim community.
As well as vigils outside mosques in Christchurch and Hamilton, hundreds gathered in the Octagon in Dunedin last night.
Earlier Saturday, thousands of people packed a vigil at Auckland's Aotea Square.
A public vigil will be held in Wellington tonight in Civic Square.
Are the risks limited to Christchurch?
Police said there was no guarantee the risk was limited to Canterbury and all New Zealanders needed to be extra vigilant. There is a heightened police presence nationwide.
Anyone who sees suspicious activity should call 111 immediately.
Distressing materials related to the attack are circulating online and police remind people it is an offence to distribute an objectionable publication. This is punishable by imprisonment.
Police said there would be a heightened police presence at community events today for safety and reassurance and dozens more officers would be moved to the Canterbury region.
What the prime minister said
Ms Ardern said that New Zealand gun laws would change and the government would move swiftly on that.
Tarrant was in possession of a gun licence. Five guns were used in the attack, including two semi-automatic weapons and two shotguns.
A Givealittle page has been set up for victims and their families following the attack. By about 3pm on Monday it had raised more than $3.6 million.
Those who have a missing family member are urged to go the Restoring Family Links (RFL) website, where they can register missing persons or register themselves as alive.
Missing persons can also be registered on 0800 115 019. A member of the police will be in contact thereafter.
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