Three people died, two were missing and several others were injured in an explosion on a refugee boat off Australia's northwest coast on Thursday, police said.
The vessel was being towed by an Australian navy ship after it had been intercepted when there was an explosion in the engine room, said Sergeant Greg Lambert.
"It is believed that three people have been killed, two people are missing and others are injured," Lambert told Australian Associated Press. He said the precise number of injured was not yet known.
A spokeswoman for the Royal Darwin Hospital said staff had been told three people were dead and there were 46 unspecified casualties after the explosion, the Australian Broadcasting Corporation reported.
The boat was carrying 49 refugees believed to be from Afghanistan, officials said.
Home Affairs Minister Bob Debus said it was being towed to an immigration detention centre on Christmas Island, 2,600 kilometres (1,600 miles) northwest of Australia's mainland.
"The vessel was being escorted to Christmas Island so that safety and health checks could be done," Debus said in a statement.
"Border protection agencies have reported that there has been an explosion or serious fire on board this vessel."
"There are reports from personnel on the scene that this incident has resulted in fatalities, serious injuries and that a number of occupants of the vessel are missing."
Royal Darwin Hospital's critical care and trauma unit was on high alert, the spokeswoman told the ABC, while doctors in Broome city had reportedly been told to prepare for a significant number of casualties.
Six boats carrying more than 250 illegal entrants have been intercepted off or landed on Australia's coast since January, a "surge" the opposition party has blamed on the centre-left government's softening of refugee policy.
The number compares with 179 people intercepted in the whole of 2008 and follows the scrapping of a widely-criticised system under which asylum seekers, including children, were held in detention centres for years.
Prime Minister Kevin Rudd's Labor government, which came to power in late 2007, also scrapped the so-called "Pacific Solution" under which boatpeople were sent to special detention centres on the tiny island nation of Nauru or the Papua New Guinea island of Manus.
Asylum-seekers arriving by boat are still held on Christmas Island, but their claims must be expedited, with six-monthly case reviews by an ombudsman now government policy.
The latest incident comes a day after ministers and officials from more than 60 countries gathered on the Indonesian island of Bali to discuss the problem of people smuggling.
Australia's Foreign Minister Stephen Smith told the meeting that increasing numbers of jobseekers were being pushed into the hands of people traffickers as the economic downturn forced them to migrate in search of work.