NZ cabinet agrees tougher gun laws in 'principle'

New Zealand's cabinet agreed measures to tighten gun control laws "in principle" today, just days after a deadly mass shooting killed more than 50 people.

Prime Minister Jacinda Ardern said details of the measures would be rolled out before a cabinet meeting next Monday, saying "the time to act is now".

Ardern also announced an inquiry into Friday's twin mosque attack in Christchurch, which raised questions about how the suspected gunman -- a white supremacist -- was not picked up by intelligence agencies.

Although details have yet to be hashed out, the speed of New Zealand's move has resonated around the world -- particularly in the United States, where reforms have spluttered for decades, and similar debates are re-run after each new mass shooting.

It took us 72 hours, Ardern said.

"We have made a decision as a cabinet, we are unified," she added, flanked by her coalition partner and deputy prime minister, Winston Peters.

Peters, whose New Zealand First party has previously opposed changes, said he backed the prime minister fully.

"The reality is that after one pm on Friday our world changed forever and so will our laws," he said.