The Asia Pacific director for the UN High Commissioner for Refugees, Indrika Ratwatte is the most senior United Nations official to see Australia's offshore processing facilities for asylum seekers firsthand.
His assessment is damning.
Mr Ratwatte says some refugees on Nauru are in worse shape than the 700,000 Rohingya refugees from Myanmar driven into neighbouring Bangladesh.
And the United Nations has likened that crackdown by Myanmar's army to ethnic cleansing.
"I have worked in quite a few places over the years in emergency situations. I most recently was in Bangladesh, where we have a million refugees who have crossed over from Myanmar. And looking at the conditions here -- particularly, the mental-health situation -- it's very, very shocking. Clinical psychiatrists and others have said that this is one of the places where you have the highest level of stress and trauma and post-traumatic stress amongst the population."
Mr Ratwatte says about 40 children on Nauru have spent their entire lives in detention and another 50 have spent half their lives there.
And he says keeping people on Nauru is leading to family separation.
"I have seen a little girl of 14 years old with her father in Nauru where the mother and her siblings are in Australia for medical treatment. This little girl was in a catatonic state, (this girl) who hasn't gotten out of her room in months, who has not taken a shower and who is in a state of complete stress and trauma. These situations need to be avoided."
Last week, a reportedly suicidal 10-year-old boy living on Nauru was transported to Australia and given medical attention.
That was despite calls for him to remain on the island from Home Affairs Minister Peter Dutton, who argued there were adequate healthcare options on Nauru.
Mr Ratwatte says the path of self-harm and suicide is symptomatic of the situation in the detention centre.
Mr Ratwatte says he understands the Australian government's position that offshore detention prevents deaths at sea but it also has a responsibility to people once they are on land.
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