The cases have come to light after the High Court ruled Aboriginal and Torres Strait Islander people born overseas could not be deported for committing serious crimes.
Home Affairs lawyer Pip de Veau said the department was aware of most cases before the High Court ruling last month, but some detainees had identified as indigenous since the decision.
“Negotiations are ongoing to establish evidence in a number of matters,” de Veau told a Senate estimates hearing.
One indigenous person was released from immigration detention last week.
“I can advise that one person clearly met the (indigeneity) test to the satisfaction of one of my officers and they were released during the course of last week,” Home Affairs secretary Mike Pezzullo told the committee.
Pezzullo said if detainees proved they were indigenous, Home Affairs could not keep them locked up.
“There’d be an absence of power to detain a person in those circumstances,” he said.
Last month, the High Court ruled Aboriginal Australians could not be considered “aliens” under the constitution, and therefore could not be deported.
The four-three decision was a big victory for New Zealand-born Brendan Thoms, who was immediately released from detention.
But the court could not reach an agreement on whether Papua New Guinea-born Daniel Love was indigenous.
Home Affairs Minister Peter Dutton has repeatedly criticised the court’s decision, claiming it will undermine the integrity of Australia’s migration system.
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