Asylum seekers have been locked up in cells with hardened criminals - with one man spending more than three years in prison before being granted refugee status.
Advocates say New Zealand could be breaching our international human rights obligations and will release a landmark report on the practice on Tuesday.
Mt Eden Prison is where New Zealand detains some of its most dangerous criminals - and locked up with them are asylum seekers, which Tim Maurice from the Asylum Seekers Support Trust does not agree with.
"That's double-bunking with convicted murderers or rapists; often there's a lot of gang members involved, and asylum seekers are people who've come here looking for safety," he told Newshub.
An asylum seeker Newshub spoke to says he came to New Zealand at the age of 20 on a fake passport, having fled war in his country. He claimed asylum and was detained.
"I was crying day and night - I didn't know what to do," he told Newshub.
He did not want to be identified, saying he's afraid his family back home will be harmed if he is.
"It was very stressful thinking... it affects me a lot during that time I was there."
He spent seven months in Mt Eden while his asylum claim was considered.
"The cellmate I got was a very big man - bigger than me. He was shouting at me that I cannot pray."
One man spent 1178 days - more than three years - in Waikeria Prison. There are currently two asylum seekers behind bars.
"As a Kiwi I think that we would look after people coming here looking for safety rather than putting them in prison," says Maurice.
"The UN charter that we signed up for says that if people come here - however they come here - seeking asylum, we should look after them, and putting them in prison isn't looking after them."
Immigration NZ refused an interview but in a statement told Newshub the majority of asylum seekers are not detained. The reason some are is because there's a question about their identity.
"We understand that some of them will come on false documents - it's the only way they can escape from their country," says Maurice.
Amnesty International will release a report into the detention of asylum seekers on Tuesday.
"There are absolutely solutions for this so it's really just up to the will of the Government to ensure they're not breaking human rights law," says Meg de Ronde, executive director of Amnesty International NZ.
Advocates want asylum seekers to stay at the Māngere Refugee Centre instead of people locked up, and only for a maximum of 28 days - even if it takes officials longer to sort out their paperwork.
But Immigration Minister Kris Faafoi says he has no plans to change how asylum seeker cases are handled, and the Government complies with human rights conventions.
