Prime Minister Jacinda Ardern says details of reforms to New Zealand's gun laws will be announced within 10 days of Friday's Christchurch mosque attacks.

Photo: RNZ / Rebekah Parsons-King

Ms Ardern said although in principle decisions have been made around the reform of New Zealand's gun laws following today's Cabinet meeting there is still some detail to be worked through.

The Green Party joined meetings today with Labour and NZ First to talk about reform of New Zealand's gun laws.

Watch the post-cabinet press conference here:

Ms Ardern said she intends to give more information to the media and public before Cabinet meets again next Monday, within 10 days of the attacks.

"As the Cabinet we were absolutely unified and very clear, the terror attack in Christchurch on Friday was the worst act of terrorism on our shores, it was in fact one of the worst globally in recent times, it has exposed a range of weaknesses in New Zealand's gun laws."

Ms Ardern said the work being done was not directed at those New Zealand gun owners who owned them for legitimate reasons. However, she said that people are able to surrender their guns to police at any time and she would encourage them to do so if they are thinking about that.

The Police Association has called for semi-automatic weapons to be banned.

Fifty people have died in the shootings at Al Noor and Linwood Mosques and a further 50 are injured.

Brenton Tarrant, 28, has been charged with murder and has appeared in the Christchurch District Court.

The government would now be working to finalise the details of the decision made by Cabinet and its consequences, Ms Ardern said.

There will be an inquiry into the specific circumstances that lead to the mosque attacks and what the relevant agencies knew about the individual and the accused's activities. The inquiry will look into the New Zealand Security Intelligence Service (NZSIS), Government Communications Security Bureau (GCSB), police, Customs and Immigration.

Ms Ardern said the inquiry would also look at the individual's travel movement and his social media usage.

The terms of reference are being finalised and Ms Ardern said it could be a royal commission, public inquiry or ministerial enquiry.

Ms Ardern will return to Christchurch on Wednesday to meet with first responders to the attacks, including St John's ambulance and front-line support staff, as well as with family members.

There have been more than 500 calls to a help service where people can call or text 1737 to access help to specialist support if they have mental health concerns, Ms Ardern said.