Detainees, even those recognised as genuine refugees, can spend up to five years at the centres under Labor's policy of ensuring that asylum seekers arriving by boat gain no advantage over those applying through official channels.
This week, as three asylum seekers were rescued from the sea off Manus Island after a failed escape, serious allegations and complaints were raised in a report by the UN High Commissioner for Refugees and a nurse who worked at the Nauru centre. The PNG Opposition is also pursuing action in the National Court in a bid to shut down Manus Island, which it claims was set up after "many abuses of PNG law and ministerial powers".
In a report released last December the UNHCR condemned the Nauru centre for failing to meet international standards of protection, with harsh conditions giving little natural protection from the tropical heat.
It said a number of detainees were suffering the effects of pre-existing trauma and torture, but health providers on Nauru had limited capacity to help them.
Uncertainty and delays over their futures were also likely to damage mental and physical health, with widespread depression and self-harm among detainees.
Marianne Evers, a nurse of more than 40 years' experience who worked on Nauru, has told ABC television that she treated cases of self-harm, saw suicide attempts and heard allegations of rape during her time there.
"I actually liken it to a concentration camp, but the Australians don't have the guts to kill these people and put them out of their misery," she said.
"There is absolutely nothing to do. There are no trees. There is no grass. There is not even that many birds there. So we live in that heat without air conditioning in tents."
Her claims were denied by the Immigration Department.
A UNHCR report on Manus Island, completed after officials visited last month and released this week, reached conclusions similar to its earlier Nauru findings.
It said the Australian and PNG governments had breached their international human rights obligations.
The report said the damaging practice of detaining children should end as a matter of priority and criticised the lack of a legal framework for assessing claims in PNG.
Shelters too hot to sleep in
UNHCR described living conditions on Manus Island as harsh.
Couples and families lived in 3m by 3m "dongas" similar to shipping containers, many without doors or blinds, and so hot that people slept outside under a roofed breezeway.
Single men lived in 4m by 4m canvas tents, with 13 in a marquee that had neither floor nor full sides, a leaky roof, no lights, and no protection from mosquitoes.
The 66 single men had only one toilet between them.
