The accused terrorist in the New Zealand mosque attacks sent Prime Minister Jacinda Ardern his 74-page diatribe against foreign "invaders" minutes before he launched the assault that killed at least 50 worshippers.

Ardern said her office and others were emailed the alleged terrorist's so-called manifesto nine minutes before the attacks began, but there wasn't enough time to take action to stop the massacre.

"It did not include a location. It did not include specific details... If we could have [stopped it], we absolutely would have," she told reporters on Sunday.

"This was received by over 30 recipients nine minutes before guns were fired. Within two minutes of receipt it went to our parliamentary security," said Ardern. "But again, by the advice of police, by the time those emails were received they were already receiving 911 calls and responding, and someone was taken into custody within 36 minutes."

In emotional scenes, Ardern earlier met mourning members of the Muslim community in Wellington.

Friday's attack, which Ardern labelled as "terrorism", was the worst ever peacetime mass killing in New Zealand and the country raised its security threat level to the highest.