An asylum-seeker boat carrying an estimated 150 people capsized on Wednesday en route to Australia's Christmas Island, the Australian Maritime Safety Authority said.
"A vessel has capsized 107 nautical miles north of Christmas Island, there are reportedly 150 people on board," an AMSA spokeswoman told AFP.
"We don't have numbers on survivors at this stage."
The incident comes barely a week after another boat with around 200 people on board went down in the Indian Ocean as it made its way to Australia.
Rescuers managed to save 110 people and 17 bodies were recovered, but no other survivors have been found.
"There are two merchant vessels on the scene, they are recovering survivors," the AMSA spokeswoman said of Wednesday's disaster.
"We expect the HMAS Maitland to arrive on the scene in approx two hours and another defence vessel to arrive later in the afternoon."
The capsize is the latest in a series of refugee boat disasters in recent years, as rickety, overloaded vessels packed with desperate migrants struggle to reach Australia.
Most boats originate in Indonesia, though there has been a spike in attempts from Sri Lanka.
Though they come in relatively small numbers by global standards, asylum-seekers are a sensitive political issue in Australia, dominating 2010 elections due to a record 6,555 arrivals.