Winston Peters is calling for the Christchurch mosque terrorist's life sentence to be carried out in Australia, but Jacinda Ardern says now is not the time for those discussions. 

The New Zealand First leader welcomed the life without parole sentence of the Australian-born terrorist issued on Thursday at the Christchurch High Court, and said he hoped it helps with the healing of those affected. 

"The judgement is the only one that matched the depravity of the terrorist's crimes against the Islamic community and its devastating effect on all people living in this country," Peters said. 

But he said New Zealand First believes Brenton Tarrant's sentence should not be carried out on New Zealand soil at the expense of the taxpayer. 

"New Zealand First believes this terrorist should be returned to the country that raised him. Now is the time for Australia's Minister of Home Affairs, Peter Dutton, to receive and carry out the terrorist's sentence in Australia," Peters said. 

"The Islamic community and all of New Zealand have already suffered enough without having to pay astronomical prison costs to keep him safe in our prison system."

Prime Minister Jacinda Ardern also welcomed Justice Cameron Mander's sentencing of Tarrant, but says now is not the time to be discussing a prisoner transfer. 

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"I do feel like today probably isn't the day for too much discussion around that. I feel like today deserves to be the day for those families to hear that sentence be handed down and just to have a bit of time with that," she said. 

"The one thing I should say, though, is that there isn't currently a legal basis for it so it would be a very complex undertaking. I think the thing though - more than even just the legal basis for it - that I would be most interested in is the views of the families. 

"I think they've rightly prioritised this process - the sentencing - and so that's not a question I've asked them yet, but their view will be a big driver for me as to whether or not that's something we consider. 

Australian Prime Minister Scott Morrison said on Thursday Ardern had not raised with him the prospect of a prisoner transfer.

"It's normal practice that criminals convicted of these offences serve their sentences in that jurisdiction, and that's my understanding of what the arrangements are and no request has been made to Australia for that to be any different."

Ardern has previously raised the idea of transferring Tarrant to Australia, but only after "justice is done" in New Zealand first. 

New Zealand law professor Alexander Gillespie, writing in The Conversation, recently called for a new prisoner transfer agreement to send Tarrant home to Australia because of the huge cost to New Zealand of keeping the terrorist locked up. 

"The next two years alone will cost New Zealand taxpayers about $3.6 million," Prof Gillespie wrote. "If he has a normal life span the cost may be in the tens of millions per decade."

Cabinet papers from July 2020 showed $1.9 million had been approved to keep him behind bars for this fiscal year, with a further $1.6 million for next year and 2021. 

Funding has also been allocated for screening prisoner mail after Newshub revealed last year Tarrant had sent a letter that ended up on an online white supremacist message board. 

Prof Gillespie pointed out that hundreds of Kiwi ex-prisoners have been deported back to New Zealand from Australia, despite many of them having no connection to the country. 

Ardern has repeatedly flagged it with Morrison. 

The pair held a press conference Sydney back in February, during which Ardern told Morrison in front of the media: "Send back Kiwis, genuine Kiwis - do not deport your people, and your problems."

Morrison said Australia had no intention of changing its deportation policy. 

Prof Gillespie said Australia and New Zealand have the chance to make a better deal and form a better relationship by signing a prisoner transfer agreement that suits both nations.