Australia holds refugees and asylum seekers arriving by boat on PNG's Manus Island and the Pacific nation of Nauru.
The Manus center is due to close next week. Australia has set up alternative accommodation in a nearby town.
A Human Rights Watch report said asylum seekers risked suffering "unchecked violence" in PNG after the closure.
The group, which visited the island in September, said refugees and asylum seekers had been attacked by local men "sometimes armed with sticks, rocks, knives, or screwdrivers".