The St Vincent de Paul Society has called on its Australian members to write to Prime Minister Malcolm Turnbull and express their "deep and urgent" concern for the safety of 600 men who remain in the Australian refugee processing centre on Manus Island in Papua New Guinea.

The 600 men have refused to leave the centre which closed more than a week ago. Earlier this week, Papua New Guinea's Supreme Court rejected an application to restore services to the centre, reportedly saying there was no good reason why the men should not move to alternative accommodation in the town of Lorengau. Some of the men have reportedly said they feared for their safety should they leave the centre.

John Falzon, CEO of the lay Catholic organisation, said reports from members on the ground at Manus indicate a "deteriorating and dangerous situation". "Many of the men who have been detained are vulnerable with a variety of health problems that cannot be treated adequately on Manus," he said.

Dr Falzon said it is "unconscionable" that Australia has created the situation by detaining men who had come to us to seek refuge in a foreign country. "We are now further adding to their suffering by abandoning them in a dangerous situation without adequate food, water or health care."

In a 'call to action', the society are calling on members to express their concern in letters to the Prime Minister and federal MPs.

Earlier this week, Rev Peter Catt, chair of the Australian Churches Refugee Taskforce, said Australia's offshore detention policies had, for a second time, "created a serious breach of human rights and a devastating fear for those who are experiencing it".

"The situation on Manus Island PNG is clearly not safe for the refugees living there," he said. "Rather than blaming the local Manus island residents, it must be acknowledged that Australian Government leaders over the past four years have failed to recognise the dangers of warehousing refugees in communities and countries who have their own disadvantage, struggles and conflicts."

Last weekend, a spokesman for the UN High Commissioner for Refugees said the organisation had "serious concerns about the welfare, safety and wellbeing" of the 600 men.

Prime Minister Turnbull told the ABC this week that the alternative facilities for the men were of a "very high quality" and they should relocate.