An asylum seeker boat has capsized 172km north of Christmas Island with about 150 people on board. The boat has since sunk, according to Australian Customs and Border Protection.
Australian Prime Minister Julia Gillard says her best advice is that 123 people have been rescued so far.
The HMAS Maitland has arrived at the scene and a Royal Australian Air Force maritime patrol aircraft carrying life rafts is on its way.
Two merchant vessels arrived at the site hours earlier and began rescuing survivors, said Australian Maritime Safety Authority spokeswoman Jo Meehan. She could not say how many survivors there are.
The initial distress call was made at about 6:20am, reports ABC News.
This accident comes only days after another boat carrying more than 200 asylum seekers capsized in the same area - about 90 people were killed.
"This is obviously another grim day to our north. We've had two disasters at sea in less than a week as the boats just keep coming and coming and coming," said Australia's Opposition leader Tony Abbott.
Australia is a common destination for boats carrying asylum seekers from Afghanistan, Iraq, Sri Lanka and other poor or war-torn countries.
3 News / AP