Refugees and asylum seekers marooned on Manus Island are at grave risk of an impending mental health crisis, a coalition of humanitarian agencies is warning Australia's political leaders.

We are robbing them of their freedom, denying them all hope and condemning them to terrible suffering.

Advocates who have just returned from a week in Papua New Guinea have delivered a bleak assessment about the "most insidious and deep impact" indefinite detention is having on about 600 men.

World Vision chief advocate Tim Costello described meeting men on Manus Island with fear and anxiety written across their faces and whose bodies were frozen in fear.

The last of about 300 men refusing to leave the now-closed detention facility were forcibly removed on Friday, ending a tense three-week stand-off.

They joined hundreds of others already moved to alternative accommodation sites.

Immigration Minister Peter Dutton maintains the alternative sites are equipped to handle men from the decommissioned detention center.

Mr. Dutton pinned the problem on those who wanted refugees and non-refugees brought to Australia, insisting that would never happen.

But for the agencies, more pressing than the unprepared housing is the mental health and wellbeing of the men being held there.

Read the full article on the potential mental health crisis in Manus at SBS