Asylum seekers doused boat in petrol before deadly explosion

Asylum seekers rescued from their vessel after this morning's explosion were transferred to HMAS Albany (pictured) and HMAS Childers. Photo / Supplied

PERTH - Asylum seekers doused their boat in petrol before a fatal dawn explosion off the northwest Australian coast, West Australian Premier Colin Barnett says.

Mr Barnett said it was unclear how the flames ignited.

"It is understood that the refugees on the boat spread petrol and that ignited causing the explosion," Mr Barnett told reporters in Perth.

Mr Barnett would not elaborate on the claim when questioned further.

At least three asylum seekers were killed in the incident about 6.30am (10.30am NSZT) today.

It is believed the explosion occurred in the engine compartment of the boat as a navy vessel was towing it to Christmas Island off WA.

Some defence personnel received minor injuries in the explosion but were not among the dead.

The vessel sank soon after the explosion and the asylum seekers were transferred to HMAS Albany and HMAS Childers.

The boat, with 49 people on board, was intercepted off Ashmore Reef on Wednesday. They are thought to be from Afghanistan.

Mr Barnett said the incident was a test of the Rudd government's border protection policies.

"It would seem that these are sophisticated operations and it is almost a test of the Rudd government, I think they are testing the relatively new Rudd government," he said.

"We are a safe haven, a prosperous developed nation in a very dangerous part of the world.

"We can expect Australia's borders will be under continued pressure."

WA Assistant Police Commissioner John McRoberts said he understood the boat was moored at the time of explosion.

"Now I don't know why it was moored, it was perhaps because they were assessing what to do with the vessel and the occupants," he told reporters.

The seriously injured were likely to be airlifted to Truscott Island, off Kununurra, off WA's northwest, he said.

"The advice we have is that the naval vessels are heading towards Darwin but it is likely that using air assets, the more seriously injured will be taken to Truscott Island where they will be stabilised," he said.

"It is most likely that those will burns will go to Royal Perth Hospital and the other injured to Darwin Hospital."

Mr McRoberts said the explosion took place in commonwealth waters, 840km west of Darwin and 610km north of Broome.

The area falls under the Northern Territory police jurisdiction.

"The incident in theory has taken place in commonwealth waters but for coronial investigations and in fact should it indeed be a criminal investigation it is actually in the Northern Territory police jurisdiction," Mr McRoberts told ABC radio.

Any coronial inquiry would be held in the NT.

WA police had offered assistance in the investigation, Mr McRoberts said.

- AAP