The Federal Government has flagged the closure of the Port Hedland detention centre in the country's remote north-west as numbers in the centre dwindle and boats fail to reach Australia.

No boatloads of asylum seekers en route to Australia have been seen since December 17, 2001, and the government can accommodate all arrivals in the new, larger Baxter detention centre.

A spokesman for Immigration Minister Philip Ruddock said that if the two trends continued, the government would be faced with an "economic decision".

"Given that Baxter can still handle about 800 people, we could consolidate everybody in the right centre right now," the spokesman said.

"It probably has got to the point where it's uneconomic to run three centres."

Three mainland detention centres are home to asylum seekers who travelled to Australian territory by boat. The three isolated centres are Baxter and Woomera in South Australia, and Port Hedland in Western Australia.

The three centres house about 480 detainees, well below Baxter's 800 capacity.

Near the South Australian town of Port Augusta, Baxter is a former army camp converted into nine compounds. The $43 million Baxter centre only took its first detainees in early September last year. Four months later arsonists used mattresses, cupboards and shower curtains to start blazes that caused an estimated $2 million damage and destroyed 77 rooms. The spokesman said that for Woomera and Port Hedland detention centres to be closed, the residential housing project that accommodates children and women from Woomera would have to be replaced by another residential project. "If we can get a residential housing project at one of the other centres, and possibly Baxter is most likely, or the preferred, that would pave the way for Woomera to be mothballed," he said.