Up to 100 people are feared dead after a boat believed to be carrying refugees from Afghanistan to Australia capsized north of Christmas Island last night.
Officials say 109 people, many of them injured, have been rescued alive while a number of bodies have been pulled from the water.
Indonesian authorities are leading the rescue effort for the boat that went down in their jurisdiction, but treacherous conditions with waves up to 12 metres high are continuing to make it hard for rescuers to find survivors.
The Australian Maritime Safety Authority says search and rescue operations are continuing tonight, with a search plane locating more debris and lifejackets in the area late this afternoon.
Christmas Island acting administrator Steven Clay said the island's emergency management plan had been activated.
"Christmas Island is a fairly small hospital by normal standards," Clay said.
"It's a remote community and it's not meant to cater for that sort of emergency but we will deal with it the best we can."
Australian Home Affairs Minister Jason Clare said about 40 survivors were found clinging to the upturned hull of the boat.
"One survivor is reported to be a 13-year-old boy, the remainder are reported to be all adults," he said.
Boat response time "appropriate"
The Federal Government has defended the rescue response after questions were raised about events leading up to the tragedy.
The government first received a distress call late on Tuesday
and again early on Wednesday.
However, the boat was advised to return to Indonesia because it was nearer to that country.
Clare told ABC Radio on Friday a surveillance plane also spotted the boat on Wednesday afternoon.
But it wasn't until late on Thursday afternoon that an RAAF aircraft arrived at the scene and started dropping liferafts.
Clare said the response to the emergency had been appropriate. He said the information from the aircraft was that there was no visual sign of distress from the boat.
"Nevertheless, Christmas Island Border Protection Command began to pre-position vessels to respond when an urgent request for assistance was requested."
Asylum seekers are a hot political issue in Australia. So far this year, more than 50 boats carrying more than 4,000 asylum seekers have been detected by Australian authorities.
Refugees seeking asylum in Australia often set sail from Indonesia heading for Australia's Indian Ocean territory of Christmas Island in dangerous and overcrowded boats, with the help of people smugglers.
In December 2011, as many as 200 died when an overcrowded boat sank off the coast of East Java. In 2010, 50 asylum seekers died when their boat was thrown onto rocks at Christmas Island.
In 2001, a crowded boat known as the SIEV X sank on its way to
Australia with the loss of 350 lives.