New Zealand security services did not focus enough on the threat from right-wing terror in the run-up to 2019's Christchurch mosque attacks, but could only have prevented the murders "by chance," an inquiry reported on Tuesday.

Brenton Tarrant, the gunman who shot and killed worshippers in the Christchurch mosque attacks, is seen during his sentencing at the High Court in Christchurch, New Zealand on Monday. Photo: VCG

The royal commission - the most powerful judicial probe available under New Zealand law - called for sweeping changes to counter-terrorism operations in response to the white supremacist attack in which 51 Muslim worshippers died. 

The 800-page report said spy agencies had placed an "inappropriate" focus on Islamist extremism before the attack and did not sufficiently explore the right-wing terror threat.

But it stopped short of saying authorities could have prevented the massacre, finding that the "fragmentary" information available about lone-wolf shooter Brenton Tarrant prior to the killings was not enough to mark him as a threat.

"There was no plausible way he could have been detected except by chance," said the report on the March 2019 attack, in which Tarrant targeted men, women and children who had gathered for Friday prayers in the South Island city.

New Zealand Prime Minister Jacinda Ardern welcomed the review and vowed to look at all 44 recommendations.

She said another major criticism in the report - lax firearms law enforcement that allowed Tarrant to amass an arsenal of military-style semi-automatic weapons - had already been addressed by her government.
Newspaper headline: NZ mosque attacks found unpreventable