Nearly 200 New Zealanders are being held in an Australian detention centres including on Christmas Island, Prime Minister John Key says.

The isolated island, an Australian territory that lies south of Java, Indonesia, has long been used to detain asylum seekers.

However, New Zealanders who have previously served jail time in Australia are now being sent there and held for months.

This afternoon Mr Key said about 196 New Zealanders were in seven Australian detention centres.

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"It seems as if people are obviously transitioning from whatever corrections facility they were in, to potentially a place like Christmas Island, and then coming back to New Zealand," he said.

"What I don't have is good information on whether those numbers are going to grow a lot, how long they're actually there, what sorts of people are going there. So we are trying to get better information."

The Prime Minister said, ultimately, New Zealand could not stop Australia making changes to its policy on deportations.

"There has been a change in Prime Minister...we will have those conversations with Malcolm Turnbull."

He believed New Zealand still had a special relationship with Australia, and thought it was likely Kiwis were "collateral damage" in a broader policy shift.

Mr Key sought details after yesterday admitting he did not know detainee numbers, or why exactly they were being held.

He was concerned about Australia toughening up its rules, and making non-citizens who served more than a year in prison liable for deportation.

That meant there were some people facing deportation who had lived in Australia for many years and who committed relatively minor offences.

Concerns have been mounting about people, including New Zealanders, held in detention centres, with a member of the Australian Lawyers Alliance saying their treatment could amount to torture.

"We have been advocating on this issue for some time, because what has been happening is effectively a person's right to a fair trial, their right to be with their family...fundamental rights have been stripped from them," Australian barrister Greg Barns told Radio New Zealand, and added such detentions violated Australia's obligations under international law.

"It probably gets into the situation where the form of imprisonment and the form of detention, given where it is, and the fact that it strips people from their families, is probably getting into the area of torture and other unusual forms of punishment."

Mr Barns said that, at the federal level, Australia did not have human rights legislation.

Labour's Foreign Affairs spokesman David Shearer said New Zealand needed to apply pressure to sort out the issue, because if it was not resolved quickly it could sour the Trans-Tasman relationship.

Mr Shearer said he suspected Australia's laws were targeted at other groups, and New Zealanders who had lived long-term in Australia had been caught up in that net.

"[They] for all intents and purposes consider themselves Australians. They will certainly be cheering for the Wallabies in the World Cup.

"I am hoping that it is unintended, that is something that wasn't foreseen when the legislation went through, and that it is something we can fix pretty quickly."

Mr Shearer said he had concerns about how seriously National were taking the issue.

"John Key two weeks ago said he didn't have any details in front of him. When he was asked yesterday he said, again, he didn't have any details.

"He has got to know, and he has got to be quite forceful in saying, 'we don't believe this is acceptable or in according with the principles of natural justice.'"