Options for a national day of mourning being discussed - Prime Minister Jacinda Ardern

Prime Minister Jacinda Ardern is yet to commit to a date for a national day of mourning in the wake of the Christchurch terror attack.

Speaking to The AM Show, Ardern said vigils are already happening and people are united in their grief.

"I want to create the space for families to be able to mourn their lost loved ones. That will obviously be happening over the course of this week."

Ardern said she would discuss with Cabinet today options for people to gather as a nation to mourn.

"I'll look soon to provide some sense of when we would look to have a memorial as a nation, but that timing will factor that families are yet to bury their lost loved ones."

Middle East specialist at Otago University Professor Bill Harris told The AM Show a national day of mourning will show that New Zealanders take the attack very seriously and would bring the rest of the West into line. He made mention of the lack of international delegation to come to New Zealand.

"What we've seen is the worst attack on Muslims and of mosques in the West ever in modern history.

"This is a really big event and we need to react in a way that takes that into consideration."

As New Zealanders return to work and school in the wake of the attack, Unite Union and the Migrant Workers Association have called for a national day of mourning on March 22. 

Opposition party leader Simon Bridges told The AM Show that he is in favour of a national day of mourning.

"We need to mark this and mark it seriously, we've never seen anything like this in our time," Bridges said.