Doctors kicked off Nauru say many of the detainees Australia sent to the island nation are suicidal and "devastated" children have lost all hope.
The Nauruan government forced Medecins Sans Frontieres out of the country last week, abruptly ending the group's free medical care for detainees and local Nauruans.
The organisation, also known as Doctors Without Borders, says it treated 78 refugee patients who either attempted suicide, had suicidal thoughts or inflicted self-harm.
MSF has been working independently on Nauru since November 2017.
"Five years of indefinite limbo has led to a radical deterioration of their mental health and wellbeing," MSF Australia executive director Paul McPhun told reporters in Sydney.
"Separating families, holding men, women and children on a remote island indefinitely with no hope of protection except in the case of a medical emergency, is cruel and inhumane."
Dr McPhun said the Australian government's policy of indefinite offshore detention "destroyed their resilience, shattered all hope and ultimately impacted their mental health".
He said many children are suffering traumatic withdrawal syndrome, are unable to eat, drink and talk and have lost "the will to live".
Home Affairs Minister Peter Dutton says MSF was not involved in providing medical services to immigration detainees on Nauru.
But Dr McPhun said Mr Dutton was "clearly ill-informed" because the first page of the memorandum of understanding with the Nauruan government made clear that refugees and asylum seekers would be provided services "with no discrimination".
Dr McPhun said the agreement also stated MSF would be given three months to wrap up their program in the event they were no longer needed.
Dr Beth O'Connor, who treated patients on Nauru, says MSF's relationship with the government had been declining for some time.
"I recall one incident where I was reviewing a child who had made a suicide attempt ... they did not have any other doctor under the Nauru hospital who was available to do that," she told reporters.
"During this consultation with the family, I was interrupted by a government official and told to leave."
Fellow doctor Christine Rufener questioned how the Nauruan government could meet people's mental health needs.
The hospital has no psychologists or therapists on staff, one mental health nurse who supports only Nauruan patients and one full-time psychiatrist who doesn't speak English, she said.
"Patients have told us that the police have taken refugees who have made suicidal attempts to jail instead of the hospital."
Canberra contracts International Health and Medical Services to provide mental health care to asylum seekers on Nauru but Dr Rufener said "sharing with your captor your concerns ... that's not an environment that could lead to ... recovery".
The Royal Australasian College of Physicians on Thursday said the situation on Nauru "constitutes a medical emergency" and Canberra should "immediately transfer all refugee and asylum seeker children and their families to Australia".
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