John Key says he'll be doing his best to try to get Kiwi offenders a better deal in Australia once they've finished serving their prison sentences.

As it stands, if they have served 12 months or more, they can be locked up in a detention centre at any time and then deported.

The Prime Minister will raise the issue with his Australian counterpart Malcolm Turnbull who arrives late tomorrow for talks on Saturday.

Mr Key says we treat Aussies here better than they treat Kiwis there.

"If you have been in New Zealand for 10 years or more, then ultimately, we don't deport you despite the severity of the crime."