A 13-year-old boy is among the survivors of the asylum seeker boat that capsized overnight 200km northwest of Christmas Island.
Home Affairs Minister Jason Clare says 110 passengers have been rescued while the bodies of three men have been recovered. All on board were male.
"Initial indications suggest there were approximately 200 people on the vessel," Mr Clare told reporters in Sydney.
"One survivor is reported to be a 13-year-old boy, the remainder are reported to be all adults."
The Australian Maritime Safety Authority (AMSA), which is working with Indonesia's search and rescue authority BASARNAS, says search and rescue operations are continuing.
The disaster began to unfold after 3pm (AEST) on Thursday, when an Australian Customs and Border Protection surveillance plane spotted a vessel "in distress" 200km northwest of Christmas Island.
The observers immediately contacted Indonesian authorities, who are leading the rescue effort alongside the Australian navy, defence and customs.
Mr Clare says the rescue mission was being stepped up with air patrols and four more vessels taking part.
"The objective is to save as many lives as possible," he said.
"We're still in that critical window where more lives could be saved."
He said the water temperature was 29 degrees.
"People can survive out there for up to 36 hours if they have life jackets or debris to hang on to."
HMAS Wollongong would also return to the search area after it transfers survivors onto Christmas Island.
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