Cabinet 'absolutely unified' over gun law decisions - Jacinda Ardern

Prime Minister Jacinda Ardern says Cabinet is "absolutely unified" around reforming New Zealand's gun laws - and these decisions will be unveiled within 10 days.

Ardern says a number of new Zealanders question the necessity of military-style semi-automatic weapons and the time to act is now.

She acknowledged that for a "short period" this could create uncertainty amongst gun owners, but said it was absolutely necessary.

"Within 10 days of this horrific act of terrorism we will have announce reforms which will, I believe, make our communities safer," she told media on Monday.

"It has exposed a range of weaknesses in New Zealand's gun laws."

Ardern expects the "vast majority" will agree that change needs to occur, and expects support from the gun community for her proposals.

"I want to remind people you can surrender your gun to the police at any time," she says.

"I've seen reports that people are in fact already doing this. I applaud that effort and if you're thinking about surrendering your weapon I would encourage you to do so."

Cabinet - including NZ First - was "absolutely unified", according to Ardern, and further details will be announced before the next Cabinet meeting on Monday 25 March.

Speaking alongside her, Deputy Prime Minister Winston Peters said that on Friday "our world changed forever and so will some of our laws".

An inquiry looking at the circumstances leading up to the mosque terror attack will also be launched. This will take in the SIS, GCSB, Police, Customs and Immigration, and will look at the attack could have been stopped.

It will look at accused gunman's Brenton Tarrant's travel, use of social media, and access to weapons, as well as whether there were any impediments to sharing information.