The attacker, a Sri Lankan national who had been in New Zealand for 10 years, was inspired by the Islamic State militant group and was being monitored constantly, PM Ardern said.

Friday's series of quakes was caused by tectonic movement on the boundary of the Australian and Pacific plates, part of the so-called Pacific Ring of Fire that New Zealand sits on.

Critics described the moves as 'symbolic' and would need to be backed up by greater actions to reduce emissions.

Expected to be declared next week, it is being treated as a symbolic step to improve efforts to combat global warming.

Ardern on Saturday delivered the biggest election victory for her centre-left Labour Party in half a century.

Ardern's centre-left Labour Party is on track to win 64 out of 120 seats in the unicameral parliament, the highest by any party since the country adopted a proportional voting system in 1996.

High court judge Cameron Mander said that a finite term would not be sufficient for Brenton Tarrant as he has not displayed any empathy for his victims.

An earlier election would have worked in Prime Minister Ardern's favour, as her success in stifling COVID-19 and keeping the country virus-free for 102 days until the latest outbreak had boosted her popularity.

It left 20 injured and several others missing.