"One of the roles I never anticipated and hoped never to have is to voice the grief of a nation," Prime Minister Jacinda Ardern said.

She vowed never to say the name of the 28-year-old Austalian national alleged to have killed 50 Muslim worshippers at two Christchurch mosques on Friday.

"He sought many things from his act of terror - one was notoriety and that is why you will never hear me mention his name," she said.

"He is a terrorist, he is a criminal, he is an extremist but he will,. when I speak, be nameless."

She said the victims were New Zealanders, and a nation mourned them.

National Party leader Simon Bridges said for some of the victims New Zealand had been their home for a long time, while others were immigrants or refugees.

"It was for them, as it was for us, the best litttle country in the world," he said.

"We let them down."

Deputy Prime Minister Winston Peters, leader of the government's coalition partner New Zealand First, said the attacker had tried to tear the nation apart, and had failed.

"The sickening scourage of terrorism was the work of a coward, a coward we reject."

Green Party co-leader Marama Davidson said the Muslim community had tried to warn of the dangers of anti-Islamic attitudes, and had been ignored.

"I note the Muslim voices highlighting the truth that New Zealand has a long history of colonial policy, discourse and violence that sought to harm indigenous people," she said.

At the start of the special session Speaker Trevor Mallard was joined by several religious leaders and one of them, a Muslim cleric, read a prayer.

Parliament adjourned as a mark of respect after party leaders had spoken.

Australian Associated Press