The United Nations human rights office called on Australia on Friday to restore food, water and health services to about 600 interned refugees and asylum seekers in Papua New Guinea, which Canberra cut off three days ago.

The detainees in the Manus Island Centre have defied attempts by the governments of both Australia and PNG to close the camp, saying they fear violent reprisals from the local community if they are moved to other "transit centres."

"We call on the Australian government ... who interned the men in the first place to immediately provide protection, food, water and other basic services," UN rights spokesperson Rupert Colville told a news briefing.

Australia has an obligation to do so under international human rights law and the 1951 UN Refugee Convention, he said.

There was no immediate comment from Australia or its representatives in Geneva. Its government has said the camp had been ruled illegal by PNG authorities and it had committed to supply other sites for 12 months.

Colville joined the UN High Commissioner for Refugees (UNHCR) in warning of an "unfolding humanitarian emergency" in the centre where asylum seekers began digging wells on Thursday to try to find water as their food supplies dwindled.

A refugee advocate holds a placard as she participates in a protest in central Sydney, against the treatment of asylum seekers in detention centres located in Nauru and on Manus Island, on Oct. 15. (David Gray/Reuters)

The remote Manus Island centre has been a key part of Australia's disputed immigration policy under which it refuses to allow asylum seekers arriving by boat to reach its shores, detaining them instead in PNG and Nauru in the South Pacific.

For four years, Australia has paid Papua New Guinea, its nearest neighbour, and Nauru to house asylum seekers who attempt to reach the Australian coast by boat. They include Rohingya Muslims from Myanmar, Afghans, Iranians, Sri Lankans and other nationalities, and are almost entirely men.

The impending closure of the camp is part of an Australian government plan to push refugees and asylum seekers to either return to their home country, settle in PNG or move elsewhere, thereby disbanding part of Australia's controversial and expensive offshore detention program.

Service providers and contractors have left the island, according to Australian media reports.

"We repeat our overall concerns about Australian offshore processing centres which are unsustainable, inhumane and contradictory to its human rights obligations," Colville said.

Around 500 of the men have still not had their asylum claims processed, he said.

"And obviously the sooner the better, some of them have been there I think for four years," Colville said. "So that's a very long time to sit in effectively a detention centre disguised as a regional processing centre without your case being processed."

New Zealand repeats resettlement offer

The alternative accommodation being proposed is not finished or adequate to meet their needs, including security, he said.

"We have conveyed to the Australian government and to the local government of Papua New Guinea as well that until the time the accommodation is ready, refugees should not be moved there," UNHCR spokesperson Babar Baloch said.

"But also we have urged Australia and PNG to de-escalate the situation, resume basic services - water, electricity, medical services as well."

The last food distribution was on Sunday, he said.

"Australia's policy of deterrence by rescuing people at sea, mistreating them and abandoning them has become a notion of cruelty."

<a href="https://twitter.com/hashtag/Manus?src=hash&ref_src=twsrc%5Etfw">#Manus</a> refugees digging holes to find water to drink. It’s unbearable to watch this crisis unfold. Photos via <a href="https://twitter.com/BehrouzBoochani?ref_src=twsrc%5Etfw">@BehrouzBoochani</a> <a href="https://twitter.com/hashtag/auspol?src=hash&ref_src=twsrc%5Etfw">#auspol</a> <a href="https://t.co/nnPIAvrhEK">pic.twitter.com/nnPIAvrhEK</a> —@PearsonElaine

Iranian Behrouz Boochani, who is living in the camp on Manus Island, described the conditions in a series of tweets earlier this week, saying the refugees had resorted to digging holes to try to find water to drink.

"At the moment hundreds of naked men are lying around me," wrote Boochani. "They are starving and their bodies are getting weak."

New Zealand's Prime Minister Jacinda Ardern on Friday repeated her country's offer to take up to 150 refugees.

Ardern said in a statement that the offer would be covered by New Zealand's existing refugee quota and applied to offshore refugees on both Manus Island and the tiny Pacific island nation of Nauru.

"I acknowledge that, while New Zealand has not had to contend with these issues on our shores, it's hard to ignore the human face of this situation and nor should it be ignored," wrote Ardern.

New Zealand citizens are typically allowed to work and live in Australia, a pathway that Australia fears could be used by the refugees to move to Australia.

Boochani said the New Zealand offer was "our best chance."

"Australia blocking but has no right to say no," he wrote on Twitter. "You can't keep political hostages."

Australia entered into an agreement during Barack Obama's administration for about 1,200 of those detained to be resettled in the U.S.

U.S. President Donald Trump, seemingly unaware of that history, bristled over the deal in a contentious phone call in his first days in office with Aussie PM Malcolm Turnbull, but last month it was reported that the first of the refugees were to be processed.