Scott Morrison has closed four detention centres, but will not comment on reports of a hunger strike and self-harm at Christmas Island.

The Abbott government has begun closing immigration detention centres across the country, but will not discuss rising tensions at the crowded facility on Christmas Island.

Immigration Minister Scott Morrison on Tuesday announced the closure of four detention centres, claiming the move will save the federal budget close to $90 million a year.

The Scherger facility in Queensland, the Port Augusta facility in South Australia and the Leonora facility in Western Australia will be closed by the end of next month.

The Pontville facility in Tasmania will also be formally closed and returned to Defence after sitting empty since September.

“These sites are remote, relatively small and expensive,” Mr Morrison said in a statement.

“While I acknowledge there will be an impact on some local business and service provider staff, these closures bring significant financial savings for the government and the Australian taxpayer.”

Mr Morrison says the remaining detainees in Scherger, Port Augusta and Leonora will be transferred to other facilities in the coming weeks, but the Australian Greens want more details.

“Christmas Island is already crowded, and Manus Island and Nauru are not fit to hold anybody, let alone more people,” Greens Senator Sarah Hanson-Young told reporters in Canberra.

“They should be put in community detention – that’s the cheapest option.”

The ABC reports a hunger strike is under way and half a dozen detainees have sewn their lips together at Christmas Island. But Mr Morrison is refusing to talk about the situation there.

“Commentary or publication of such activities can provide an incentive for such behaviour, which is in the best interests of people in detention to discourage,” his spokeswoman told AAP.

Deputy Prime Minister Warren Truss defended the government from fresh criticism of its secretive approach to asylum seekers, saying there was “widespread satisfaction” with the coalition’s policies.

“I think some of those who are critical of the government’s approach to asylum seekers don’t want our policy to succeed.

“They actually want open doors.”

Meanwhile, the Australian Federal Police have confirmed a 27-year-old Lebanese asylum seeker has been charged after threatening to blow up the jet that transported him from Perth to Christmas Island last week.