Two young children with New Zealand mothers are being deported from Australia under the country's tougher approach to immigration rules.

The Australian Foreign Minister, meanwhile, has agreed it would be timely to consider the treatment of New Zealanders being held in detention centres pending deportation.

Photo: RNZ / Alexander Robertson

The status of a toddler and another young child have been declared unlawful and they are currently being detained in the community.

Their mothers had a type of New Zealand citizenship - by descent - that could not be passed on to their children and they did not fall into a special visa category.

David Faulkner, who fights for the rights of New Zealanders living in Australia, said the action was being taken under existing laws that were now being enforced more rigourously.

"These cases have only just come to light recently, and when I contacted the High Commission they were as surprised as I was to hear about these matters," he said.

"It appears that [Australian] Immigration is now taking a very literal - a different hardline interpretation of the legislation."

Mr Faulkner said there could be as many as 1500 children in Australia who were unknowingly in the same position.

PM has 'blunt' chat with Australia about deportations

Australian Foreign Minister Julie Bishop said today that Australia would consider how it dealt with New Zealanders being held in detention.

About 200 New Zealanders are being held in Australian detention centres, or have been deported, since strict new visa laws were introduced last year.

Photo: RNZ / Diego Opatowski

Prime Minister John Key said this morning that Australia was challenging its relationship with New Zealand with its policy of detaining and deporting New Zealanders

He said he had had a long and "pretty blunt" conversation about the issue with Ms Bishop at this week's UN summit in New York.

He said Australia had to think about the way it treated New Zealanders, including those who had committed crimes but who had no ties to this country.

"There's people that have often spent their entire lives now in Australia, they went over there when they were very, very, young," he said.

"It's a little bit like the Australians saying, 'well, we're going to pick and choose; we're going to keep the ones we like but we're going to send back the ones we don't like'."

He said Australia had to take the rough with the smooth.

"We also deport people; but not in the sense that Australia are talking about, and I do think Australia has to think about this from the long haul in both the way New Zealanders are treated long-term in Australia, and also this issue."

Photo: RNZ / Alexander Robertson

Mr Key said Australian Prime Minister Malcolm Turnbull was new in the job and this would not be his "number one issue", but he would raise it with Mr Turnbull when he next met him.

"The ANZAC bond means that there's a special relationship there that surely means we might get some treatment that's different from other countries, and what they might do with other countries is up to them... But I think, when it comes to New Zealanders, the threshold's currently set in the wrong place."

Ms Bishop said it would be timely for Mr Turnbull to look into it.

"We are very close. There is no closer relationship than Australia and New Zealand. I think it's appropriate that we consider this matter as Prime Minister Key has asked us to do."

A new information-sharing arrangement, also announced today, means New Zealand will receive more information about pending deportations from Australia.

Calls for action on detention centre policy

One of the New Zealand government's support partners had earlier criticised it for a lack of action on New Zealanders held in Australian detention camps.

United Future leader Peter Dunne said he found it astounding that the government had not yet intervened.

"The ministerial engagement is important and given the closeness of the two countries, allegedly, and the frequency of flights between us, I would have thought either one or the other would have got on a plane pretty quickly - and gone and had a face-to-face sort out."

Mr Dunne said the deportations were out of line with the vaunted special relationship between the two countries.

Meanwhile, the sister of a New Zealand man who died in an Australian high-security prison said she was overwhelmed to hear Australian officials will investigate her brother's death.

Junior Togatuki, 23, died in isolation in the jail two weeks ago, while awaiting deportation to New Zealand after serving a sentence for robbery and assault.

New Zealand Foreign Affairs Minister Murray McCully said his Australian counterpart had assured him there would be an inquiry into the death, which officials said was suicide.