Prime Minister John Key says he understands about 200 New Zealanders are being held in seven detention centres in Australia, including on Christmas Island.
It is believed many are facing deportation because of criminal convictions.
Australian authorities have refused to release details on the number of New Zealanders being held on Christmas Island.
However, the Australian Human Rights Commission has said it is possible they are being denied access to justice.
While talking to reporters in Fielding this afternoon, Mr Key was asked, "Do you have any numbers yet, as to how many New Zealanders are on Christmas Island?"
Mr Key replied that the best advice he had was just under 200.
"So around about 196... but again, we're trying to get better information on that."
A few minutes later, Mr Key repeated those numbers: "My understanding is the numbers are lower than some of the media-reported numbers; I mean, the best advice I've had is when it comes to Christmas Island, it's only one of the camps obviously, is 196, but I take everything with a bit of a grain of salt."
After Radio New Zealand reported those comments, Mr Key's office called to correct the figures, saying it was 200 in seven detention centres across Australia.
The spokesperson said the government was not at liberty to say exactly how many New Zealanders were being detained on Christmas Island.
Mr Key said he wanted better information from Australia about how many more New Zealanders would be sent to detention centres, and how long they would be there.
He said ministers were working on a memorandum of understanding with Australia to lay out the process for New Zealanders who may end up being deported.
Christmas Island conditions 'dangerous'
Australian Human Rights Commission president Gillian Triggs said it did not make sense to transfer people to the island when they were already in custody.
She said people being detained in offshore facilities were being denied basic justice.
"I'm afraid one of the purposes of detaining people on offshore areas is, of course, that they do not have access to their lawyers, they can't see their family and friends.
"Whereas had you been charged with a crime and convicted before a court of law of that crime, you would be held in a prison in Australia where conditions would be significantly better... You would be able to contact your lawyers on a regular basis."
Professor Triggs said the United Nations had been critical about the conditions at the Christmas Island detention centre.
"[The UN special rapporteur on the torture convention said] the conditions breach the torture convention, which is an extraordinary conclusion to reach in relation to the Australian government's behaviour," she said.
"The conditions there are dangerous... I've been to Christmas Island three times, and I know what those conditions are like."
One New Zealander detained on Christmas Island said today he believed up to 50 New Zealanders were being held in the island's detention centre.
The Aucklander, who asked not to be named, who was in a Sydney prison for manufacturing ecstasy, said a group of 20 from New Zealand and the Pacific Islands were moved from a Sydney immigration detention centre yesterday, under the guise of meeting immigration officials.
But he said they were then put in solitary confinement and moved to Christmas Island.
"Normally, you go and come back to the wings - and then when I went down there, the way they were doing it, they were just surrounding you with big blokes, telling you that you're going to Christmas Island and then they're locking you straight into a segregation cell, which is like, it was like a punishment cell.
"It seems like they're getting rid of all of the Kiwis and all the big boys, you know [Pacific] Islanders."
He said his lawyer tried everything legally to get him off the plane but it was fruitless.
Another detainee, Otago-born Jason Wereta, said he was given no reason for being flown to Christmas Island in April this year.
Mr Wereta, who is being held on Christmas Island for driving offences and assault, said the sudden move meant he did not get to see his wife and children, who lived on the Gold Coast and had been planning to visit him.
"They're telling us nothing here, I've been here for six months. When I first came to Christmas Island, they told me 'do two or three months of good behaviour then we'll send you back to the mainland'.
"They take us from our families... for what reason, you know they want us to stuff up, they want us to sign the dotted line to go home back to New Zealand.
"I said, 'No, I'm fighting for my kids, I have property here, I have children here, I have my wife here, I have my dad and my brothers and sisters here - why would I want to fly home to go to New Zealand?'"
A third New Zealander detained on the island said the conditions were so poor, he was ready to surrender and be deported to New Zealand - a country he had barely lived in.
Ben Taulaga moved to Australia as a child, and has lived there for the last 17 years.
He was at a detention centre in Darwin but, after a fight with another detainee, he was transferred to Christmas Island.
He said it felt like he was being punished for his bad behaviour, and neither he nor his lawyer understood what was happening to his case.
Over 400 visas cancelled since December
The Australian Immigration Department released figures this afternoon showing 436 New Zealanders have had their visas cancelled for criminal convictions since December.
The largest number, 95, were for assault, followed by 83 for unspecified violent offences.
Drug offences number 47, armed robbery 42, and non-violent offences, 53, also feature.
One murderer makes the list for cancelled visas.
The Australian Immigration Minister has declined to be interviewed by Radio New Zealand.