The mental health of refugees detained by Australia on the Pacific island of Nauru has deteriorated so badly that some children are in a "semi-comatose state", unable to eat, drink or talk, Medecins Sans Frontieres has said.

Nauru is one of two Pacific nations where Australia detains hundreds of asylum seekers intercepted while trying to reach the country by boat, a policy widely criticised by the United Nations and rights groups.

MSF, one of the few groups to independently assess refugees at the restricted facilities, provided mental health care to asylum seekers and Nauru residents until the Pacific nation cancelled its contract on 5 October.

"During our time on the island, we witnessed a significant deterioration of mental health among our asylum seeker and refugee patients," Paul McPhun, executive director of the medical aid group, told reporters in Sydney.

Children are among those affected by mental health issues, he said, although he did not give a specific number.

"Many children exist in a semi-comatose state, unable to eat, drink and talk," Mr McPhun said, adding that some children required intravenous fluid drips.

Representatives for the government of Nauru and Australia's Minister for Home Affairs, Peter Dutton, who oversees the policy, did not immediately respond to requests for comment.

Mr Dutton told reporters yesterday he would like to resettle the Nauru refugees in Australia, but that would encourage other asylum seekers to attempt the dangerous journey by boat.

Conditions in the Nauru camp, and another facility on Papua New Guinea's Manus Island, have been criticised by the United Nations and human rights groups.

Mr McPhun said the decline in mental health among refugees on Nauru was "clearly attributable" to their indefinite detention.

"Shockingly, of the refugees we have treated, at least 78 have attempted suicide, had suicidal thoughts and attempted self-harm," he said.

Australia has stopped publishing data on the number of refugees held in both centres. Refugee advocates estimate 600 people are detained on Manus Island, and a further 500 on Nauru.