SYDNEY — Canberra is open to the idea of New Zealand sending the Australian-born gunman behind the Christchurch mosque massacre back home to serve his life sentence, Prime Minister Scott Morrison said on Friday (Aug 28).

White supremacist Brenton Tarrant was sentenced to life without parole on Thursday for the attacks on two mosques last year that killed 51 Muslim worshippers.

Soon after the punishment was handed down, New Zealand Deputy Prime Minister Winston Peters said Tarrant, 29, should be transferred to the Australian prison system.

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

Australia's Mr Morrison said he had received no request to transfer Tarrant but he was prepared to talk about the prospect with his New Zealand counterpart Jacinda Ardern.

"Whether he is held in Australia or New Zealand, look we're open to that discussion," he told Seven News television.

"That obviously has a lot of implications, these sorts of decisions. The prime minister of New Zealand and I will talk about those issues."

He said the wishes of survivors and bereaved family members would be paramount in any decision on Tarrant's future.

"Most of all we are concerned about what the views of the families would be for those affected and we want to do the right thing by them," he said.

Tarrant, a former gym instructor from the rural New South Wales town of Grafton, moved to New Zealand in 2017 and immediately started planning an attack on the country's Muslim community.

Government documents show it is costing around NZ$4,900 (S$4,450) per day to keep Tarrant behind bars, compared to NZ$302 for a regular prisoner.

The documents say he is "likely to have needs and present risk at a level of severity beyond any" managed in New Zealand before. 

Tarrant has already caused issues for prison authorities, when a letter he wrote from jail was posted on the extremist website 4Chan in August last year.

In it, Tarrant praised British fascist Oswald Mosley and warned "there is a great conflict on the horizon".

The Corrections Department apologised and promised it would not happen again.

Lawyers at Tarrant's sentencing this week revealed that in a pre-sentencing interview in April he said he had renounced his racist views and felt remorse for the attacks.

But judge Cameron Mander on Thursday rejected the gesture as "uncorroborated, self-serving and a relatively recent phenomenon", before imposing life without parole, an unprecedented sentence in New Zealand.

Tarrant is likely to be kept in isolation for his own safety at New Zealand's only maximum-security prison in Auckland, where 80 per cent of inmates are Maori or Pacific islanders. AFP