Acting Prime Minister Winston Peters says Australia's detention of a 17-year-old New Zealander in an adult deportation centre ignores United Nations agreements.
Foreign Minister Winston Peters - standing in for Jacinda Ardern who is on maternity leave - said the issue has been raised with the Australian government.
The teenager has been held in Melbourne since March, awaiting a deportation hearing this month, reportedly over non-violent offending.
Mr Peters said New Zealand and Australia were joint signatories, along with many other countries, to UN conventions on children.
"This person is regarded as a child or a minor, and I'm just reminding the Australians - you're a signatory, live up to it."
New Zealand had made it clear to Australia this country did "not like" the situation.
Mr Peters will meet with the Australian Foreign Minister Julie Bishop next month and said he would again raise it.
"The Australians are very aware what our view is on that, and the expulsion of so many New Zealanders from Australia; some who have only been in New Zealand in their total lives for three and half, four years."
Mr Peters said New Zealand had already raised this specific case with Australia through diplomatic channels.