Papua New Guinea (PNG) police have entered an abandoned Australian-run detention camp seeking to get some 380 asylum-seekers who have barricaded themselves in there to leave, two of the men told Reuters on Thursday.

One said the men felt threatened and scared and some climbed onto roofs for safety. Mostly from Afghanistan, Iran, Myanmar, Pakistan, Sri Lanka and Syria, the men in the camp are being held under Australia's strict "sovereign borders" immigration policy, under which it refuses to allow asylum seekers arriving by boat to reach its shores.

"The refugees are sitting peacefully and immigration and police are asking them to leave the prison camp," tweeted Behrouz Boochani, one of the men inside the Manus Island centre who is defying attempts by Australia and PNG to close the facility.

The asylum seekers have barricaded themselves at the closed camp because they say they fear for their safety if moved to a transit centre elsewhere on the island, and risk being resettled in PNG or another developing nation permanently.

Australia's immigration office did not have an immediate comment when contacted by Reuters.

The stand-off has attracted the attention of the United Nations, which is a long-time critic of the conditions experienced by asylum seekers held in Australia's offshore camps. Calls to PNG immigration were not immediately returned.