Australia must act to avert 'tragedy' at migrant centres: UN

Australia must act immediately to prevent further "tragedy" from unfolding at the migrant detentions centres on Papua New Guinea and Nauru, the UN said Friday, renewing its harsh criticism of Canberra.

The health situation of those being held at the two sites is "collapsing" and Australia is failing to medically evacuate all those in need of urgent care, UN refugee agency spokeswoman Catherine Stubberfield told reporters in Geneva.

One adolescent girl remains on Nauru despite having "doused herself in petrol before attempting to set herself alight and pulling chunks of hair from her head," she added.

"UNHCR does not agree with the government of Australia's assertion that such cases are solely 'matters for Papua New Guinea and Nauru,'" Stubberfield added.

She underscored that Australia "designed, financed and managed" the offshore migrant processing system.

"Australia remains responsible under International Law for those who have sought its protection." Canberra says its harsh policy of sending migrants to offshore centres is necessary to stop refugees and people smugglers from attempting the treacherous boat journey to Australia.

Since the current policy was introduced in 2013, an estimated 3,000 refugees and asylum seekers have been transferred to Papua New Guinea and Nauru, according to the UN.

About 800 are still on Nauru and 650 on Papua New Guinea.

Earlier this month, medical charity Doctors Without Borders (MSF) called for all detainees to be removed from Nauru as those held there were in a "complete state of hopelessness and despair".

That call came after Nauru's government had ordered MSF to cease its work treating asylum-seekers and locals suffering from mental health problems.

The UN has repeatedly urged Australia to accept an offer from New Zealand to take in those held in Nauru and Papua New Guinea.

UNHCR has previously made clear that it does fully understand Australia's motivation for persistently declining New Zealand's offer.

"In the absence of any other alternatives, UNHCR appeals for all refugees and asylum-seekers to be immediately brought from Papua New Guinea and Nauru to Australia, to avert further serious harm and loss of life," Stubberfield said.