SYDNEY (Reuters) - More than 1,000 people protested in Australia on Saturday against the treatment of hundreds of asylum seekers in an offshore detention center that the United Nations has described as an “unfolding humanitarian emergency”.

About 600 men have barricaded themselves inside the camp on remote Manus island in Papua New Guinea, defying efforts by Australia and PNG to shut it. Food, running water and medical services were cut off by Australia four days ago.

Australian authorities want the men moved to a transit center elsewhere on the island at the start of a process the asylum seekers fear will result in them being resettled in PNG or another developing nation.

The men also fear violent reprisals from the local community.

“These people have committed no crime other than to do what every single one of us would do if we thought our lives, or our family’s lives, were at risk,” Federal Greens lawmaker Adam Bandt told the crowd in Melbourne, Australia’s second-largest city.

Another smaller protest was staged in Sydney.

The Manus island center, and one on the tiny Pacific island of Nauru, have been key parts of Australia’s disputed “Sovereign Borders” immigration policy, under which it refuses to allow asylum seekers arriving by boat to reach its shores.

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Australia’s offshore detention policies have been heavily criticized by the United Nations and human rights groups but are backed the center-right government and the Labor opposition.

U.N. rights spokesman Rupert Colville told a news conference in Geneva on Friday about the “unfolding humanitarian emergency” in the Manus island center, where asylum seekers have been reported digging wells to try to find water.

The Australian government has not responded to Colville’s comments. It frequently does not comment on issues concerning the offshore centers, citing operational reasons.

The relocation of the men is designed as a temporary measure, allowing the United States time to complete vetting of asylum seekers as part of a refugee swap deal, agreed on last year, under which Australia will accept refugees from Central America.

Labor leader Bill Shorten has called on Prime Minister Malcolm Turnbull to consider New Zealand’s offer to take 150 refugees from the camps on Manus and Nauru.