A refugee in the Manus Island detention centre stand-off collapsed with heart pain overnight and waited more than four hours for Papua New Guinean authorities to take him to hospital.
The man is among 600 refugees and asylum seekers barricaded inside the mothballed detention centre, which closed on Tuesday.
Iranian refugee Behrouz Boochani said one of his fellow countrymen collapsed at about 7.30pm local time on Saturday.
"Some of the refugees tried to look after him and we tried to help him," Mr Boochani told AAP.
The refugees frantically tried to phone some emergency contact numbers as well as the PNG Navy and Australian Border Force trying to get help.
Mr Boochani said some refugees later flagged down a PNG police car and the officers told them to wait until morning.
"They said if anyone tries to come to pick him up they can not enter the Navy base," he said.
"Finally PNG immigration sent a car and picked up the sick refugee, after more than four-and-a-half hours since he collapsed."
Mr Boochani said the refugee was taken to Lorengau hospital half an hour away however they didn't have adequate equipment to deal with his condition.
"After a few hours without any medical treatment they sent the sick refugee back," he said.
"He is in a critical situation and needs to be examined by doctors who can help him."
The man had a long history of heart pain and had seen two specialists in Port Moresby in February who had recommended treatment in Australia but that request had been denied.
Dr Barri Phatarfod from Doctors for Refugees expressed concerns about the man's medical treatment at the hospital saying no electrocardiogram heart monitoring or blood tests were carried out.
"It is impossible to adequately assess a potential myocardial infarct in the absence of both of these investigations," she said.
"If this occurred in Australia it would be grossly negligent."
Six detainees have died on Manus Island - including one who was murdered - since it was reopened in 2012.
