Labour MP Kelvin Davis says New Zealand detainees on Christmas Island are angry, hungry and traumatised, and are considering rioting.
Mr Davis has met with eight of the detainees, who he said were being treated like terrorists.
Speaking from the isolated island, he said those being held there were being denied access to their families, and their lawyers.
Mr Davis said the conditions were terrible: inmates don't get enough food, medical attention was inadequate, and if they complained they were brutalised by the guards.
He said people tried to supplement their food by catching crabs, but were threatened with $5,000 fines.
Mr Davis said he would never forget how hopeless the detainees felt about their situation.
He said New Zealand shouldn't back Australia's bid to get on the United Nations Human Rights Council while it's treating detainees this way.