SYDNEY (AFP) - The Australian authorities used tear gas to forcibly end a two-day riot on Tuesday (Nov 10) at a migrant detention centre that left parts of it severely damaged, after police reinforcements poured in to overpower inmates reportedly armed with machetes and petrol bombs.

The reinforcements poured into remote Christmas Island on Tuesday to help quell unrest at a migrant detention centre.

"The department can confirm all areas of the Christmas Island Immigration Detention Facility are under the full and effective control of service providers and department staff," the Immigration Department said in a statement.

Five detainees were being treated for non-life threatening injuries or medical conditions but it was not known whether these were sustained during the disturbance or Tuesday's operation, it said.

Immigration Minister Peter Dutton said the damage bill would be well over A$1 million (S$1 million).

Police used tear gas and bean-bag rounds - designed to deliver an immobilising but not lethal blow - to subdue rioters. "Some force was used with a core group of detainees who had built barricades and actively resisted attempts to secure compounds, including threatened use of weapons and improvised weapons," the department said. "A full survey of damage to the centre is yet to be completed, but some common areas appear to be severely damaged."

The department said the operation to regain control of the centre, which is home to 203 asylum-seekers and non-citizens including hardened criminals, was largely achieved through negotiation. All detainees have been accounted for, it said.

"Some force was used with a core group of detainees who had built barricades and actively resisted attempts to secure compounds, including threatened use of weapons and improvised weapons," it added. "A full survey of damage to the centre is yet to be completed, but some common areas appear to be severely damaged."

Mr Dutton said the police had encountered little resistance at it retook the compound.

"The government's not going to cower in the face of some of these criminals," Mr Dutton told reporters in Canberra.

The disturbance at the Indian Ocean island centre began late on Sunday after the unexplained death of an escaped asylum-seeker, named in Australian media as Iranian-Kurdish Fazel Chegeni, with detainees starting fires after guards fled.

Detainees have complained about their treatment at the facility on the Australian territory north-west of the mainland, which currently houses 203 men, among them asylum-seekers awaiting processing and foreign citizens being deported because they have criminal convictions.

One inmate, New Zealander Tuk Whakatutu, said the detainees had fallen back into one of the detention centre's compounds, which had been surrounded by police in riot gear.

Mr Whakatutu said most inmates were hoping for a peaceful resolution but a hard-core group of 20 to 30 young men, mainly New Zealanders and Pacific islanders, were "tooled up" and determined to fight.

"I want nothing to do with it but all the young fellas are gee-d up and all they want to do is go to war with them," he told Radio New Zealand via telephone, with sirens blaring in the background.

"They've got petrol bombs, they've got machetes, they've got chainsaws, iron bars, they've got all sorts."

Mr Whakatutu said police, whose numbers were bolstered by two plane loads of reinforcements from the mainland, had warned detainees they would be shot if officers encountered armed resistance.

"I don't want to get shot for something I'm not involved in," he said.

Mr Whakatutu's comments could not be independently verified but the Australian Federal Police confirmed the immigration department had requested their help and specialist personnel had been deployed to the island.

The immigration department said in a statement that an operation was underway to restore order at the facility, noting that some detainees were "continuing to engage in non-compliant behaviour putting themselves and others at risk".

"Service provider staff are continuing to negotiate with detainees engaged in protest activity and are methodically re-entering and securing control of compounds within the centre," it said.

It said that additional damage had been caused to facilities overnight, including attempts to light fires but that these had not taken hold.

New Zealand opposition lawmaker Kelvin Davis, who last month visited the centre, claimed police appeared determined to retake the facility using force and he feared for the lives of detainees.

"To be honest, I don't know if some of them are still going to be alive in a couple of hours," he said.

"The Australians aren't interested in negotiating a peaceful resolution... they've gone to the expense of flying over reinforcements who've got to earn their money.

"So they'll go in swinging their batons."

The unrest at Christmas Island came as the United Nations' top human rights body took Australia to task over hardline policies on asylum-seekers, whom it has pushed back by the boatload and incarcerated in offshore camps.

Under Canberra's tough immigration policy, asylum-seekers arriving by boat are processed on isolated Pacific islands - Nauru and Papua New Guinea's Manus Island - rather than the Australian mainland.

As well as asylum-seekers, Christmas Island's facility is also used to hold non-citizens awaiting deportation including criminals, after Canberra began cancelling visas of those with convictions.

Australia's opposition Labor Party spokesman Richard Marles criticised the lack of information about the situation.

"We need the government out on the front foot today explaining, and the minister, explaining to the Australian people exactly what has occurred here," he told the Australian Broadcasting Corporation.