About 1,000 New Zealanders could be caught up in Australia's tough new immigration policy, Prime Minister John Key says.
Under new rules introduced late last year, anyone who is not an Australian citizen and has served more than a year in prison can be deported.
Mr Key said there were about 200 New Zealanders being detained in detention centres, with hundreds more that could be sent home.
"Those people are New Zealand citizens that have a right to come back, whatever the number is," he said.
"But it's important to think about it in the context of how many people have committed criminal activity today or people that are subjected to the policy today.
"But, of course, inevitably over time there will be more so getting a handle on these numbers is really quite challenging."
Under new rules introduced late last year, anyone who is not an Australian citizen and has been sentenced to more than a year in prison, is liable for deportation.
Mr Key says there are indications that could potentially include about 1,000 New Zealand citizens.
Mr Key said he would make a powerful argument to exempt New Zealanders from the policy when he met Australian Prime Minister Malcolm Turnbull in Auckland later this week.
Labour's foreign affairs spokesperson David Shearer said the government had been preparing for months for an influx of more than 1000 New Zealanders.
"I am surprised that the government hasn't made this public because the government has been negotiating with their Australian counterparts across five or six different Ministries, including Police, Justice, Immigration and Health - to try and work out how they are going to manage the return of these people and a thousand must have been the number that came up amongst them."