New Zealand Prime Minister Jacinda Ardern has flagged immediate changes to the country's gun laws in the wake of shootings at two mosques in Christchurch, where 50 people were killed.

Key points: Jacinda Ardern says five firearms were used in the mosque shootings

Jacinda Ardern says five firearms were used in the mosque shootings She says the shooter purchased them legally as he had a "category A" gun licence

She says the shooter purchased them legally as he had a "category A" gun licence New Zealand has attempted to change gun laws three times since 2005

Speaking at a media conference Saturday, Ms Ardern said Brenton Tarrant, the Australian man charged with murder and remanded in custody over the terrorist act, had allegedly used five firearms including two semi-automatic weapons, two shotguns and a lever-action firearm.

She said he had been in possession of a "category A" gun licence, obtained in 2017, which allowed him to legally obtain the weapons in December 2017, and that he was not on any watchlists prior to the attacks.

"While work has been done as to the chain of events that led to both the holding of this gun licence and the possession of these weapons, I can tell you one thing right now: our gun laws will change," she said.

"There have been attempts to change our laws in 2005, 2012 and after an inquiry in 2017. Now is the time for change.

"There are obviously questions being asked of how this person was able to enter the country and undertake this act of terror.

"I have instructed ODESC (Officials Committee for Domestic and External Security Coordination) to report to Cabinet on Monday on these events with a view to strengthening our systems on a range of fronts including, but not limited to, firearms, border controls, enhanced information-sharing with Australia, and any practice reinforcement of our watchlist processes."

Jacinda Ardern wore a hijab when she met with members of the Muslim community. ( Supplied: Christchurch City Council )

Before Ms Ardern's announcement, former New Zealand prime minister Helen Clark told the ABC that while the country had gun control, there was room for improvement.

"We do have gun control. People have to be fit and proper persons to have guns. But undoubtedly, the law can be strengthened and improved," she said.

"Personally, I would be surprised if the New Zealand Parliament didn't accept that challenge head on to strengthen the law.

"I think we could do better, and a tragedy like this brings that forward as a priority."

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 31 seconds 31 s Australian terrorist remanded in custody

Ms Ardern said the 28-year-old Australian had based himself in the city of Dunedin prior to the attack.

Ms Ardern said a fourth person who had been arrested while in possession of a firearm on Friday had been released, as they were a member of the public wanting to help authorities.

The two others were still being questioned.

Ms Ardern praised the police officers and emergency services involved in locking down Christchurch schools and offices, swiftly arresting the suspect, treating victims; and the defence specialists for defusing improvised explosive devices.

"Many of you may have seen the footage of the arrests, and I can only describe it as an act of bravery on behalf of all New Zealanders, and an act that shows very little regard for their own personal safety," she said.

"I also want to acknowledge ambulance staff who many will have seen acting swiftly under horrific conditions, and all medical staff who continue to work with those who are injured."