15 feared dead as boat sinks off Australia

About 15 people were feared dead on Monday after a boat carrying 39 sank in rough seas far off northwest Australia despite frantic rescue attempts by a passing merchant ship and fishing vessel.

Defence chief Angus Houston said the unidentified boat capsized and then sank after the LNG Pioneer ship and Taiwanese fishing craft responded to pleas for help in a remote area off Australia's Cocos Islands in the Indian Ocean.

It was not confirmed whether the boat was one of dozens of people-smuggling vessels that have headed to Australia this year carrying more than 1,700 asylum-seekers, many of them from Sri Lanka and Afghanistan.

"I understand when the first ship got there, this vessel was still intact," Houston said. "Somehow or other during the process of interaction between the ship and trawler and also the stricken vessel, there's been a capsize and people ended up in the water."

Some 19 people were rescued by the Bahamas-based gas tanker and fishing boat, while an air force plane dropped a life raft near another five survivors, Prime Minister Kevin RuddKevin Rudd said.

"I think it's fair to say there are grave concerns about a number of those people -- we understand there were something like 39 people on board this vessel," Rudd told media.

A rescue ship was about a day's sail from the accident site off the tiny Cocos Islands and about 2,700 kilometres (1,700 miles) from the Australian coast.

"Our assets have been deployed, we have coordinated with other vessels in the area. This is a very difficult search environment," Rudd said earlier. He refused to be drawn on whether the boat was carrying asylum-seekers.