Australian police reinforcements poured into remote Christmas Island on Tuesday to help quell unrest at a migrant detention centre, amid reports inmates had armed themselves with machetes and petrol bombs.
Immigration Minister Peter Dutton said police had already retaken some compounds at the facility and so far encountered little resistance.
"There's an operation underway. The government's not going to cower in the face of some of these criminals," Dutton told reporters in Canberra.
The disturbance at the Indian Ocean island centre began late Sunday after the unexplained death of an escaped asylum-seeker, with detainees starting fires after guards fled.
Detainees have complained about their treatment at the facility, 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.
Whakatutu said most inmates were hoping for a peaceful resolution but a hard-core group of 20-30 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." 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.
New Zealand opposition lawmaker Kelvin Davis, who last month visited the centre, claimed police appeared determined to re-take 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." Under Australia's hardline immigration policy, asylum-seekers arriving by boat are processed on isolated islands, rather than the 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.