A whistleblower who worked at the Manus Island immigration detention centre in Papua New Guinea claims detainees have been raped and abused with the full knowledge of staff.

The allegations come after the Government announced all asylum seekers arriving in Australia by boat will be processed in PNG and resettled there if found to be refugees.

SBS's Dateline program has spoken to Rod St George, a former senior manager with the security firm G4S.

Mr St George has described repeated instances of sexual abuse between asylum seekers in the single male compound.

He says victims are knowingly left in the same compound as their abusers because there are no facilities to separate them.

"There was nothing that could be done for these young men who were considered vulnerable, which in many cases is just a euphemism for men who have been raped," he said.

"They just had to stay where they were."

He says attempted suicides and self-harm are now an "almost daily" occurrence at the centre.

"I've never seen human beings so destitute, so helpless and so hopeless before," he said.

Mr St George says Immigration Department staff run the camp in a worse fashion than a prison.

"I've worked with some of the worst criminals Australia has and even they've got a clearer sense of decency than what I witnessed there," he said.

"In Australia, the facility couldn't even serve as a dog kennel. The owners would be jailed."

The Immigration Department says it is "unaware of the claims in the SBS report of unreported acts of self-harm, suicide attempts or incidents of rape at the centre".

"Since the centre opened in November there have been 23 incidents of self-harm by 21 individuals," the department said in a statement.

"One transferee alleged he'd been sexually assaulted but chose not to press charges when interviewed by the PNG police.

"There have been no reported allegations of rape."

The department says all detainees are "encouraged to report any concerns for personal safety immediately in order to assess the specific needs of the individual concerned as well as ensuring the safety of the population of the centre".

"The welfare and safety of all transferees are of the utmost importance to the Department and the government of Papua New Guinea," it added.

The ABC understands Immigration Minister Tony Burke planned to speak to the whistleblower after the SBS program aired.

Under the plan announced by Prime Minister Kevin Rudd on Friday, people arriving in Australia by boat will be processed offshore.

The Manus Island centre will be expanded, but there are fears the existing centres on Nauru and PNG will still not be big enough.

Foreign Minister Bob Carr says Australia is looking for another Pacific nation to host an offshore asylum seeker processing centre in addition to those already located in PNG and Nauru.