A BOAT believed to have been carrying up to 200 asylum seekers has capsized about 200km north of Christmas Island.
Customs and Border Protection says the vessel is in Indonesia's search-and-rescue region.
Indonesia's national search and rescue agency BASARNAS is the lead authority for co-ordinating the search and rescue, with the Australian Maritime Safety Authority co-ordinating Australia's contribution.
Customs and defence vessels are being deployed to assist.
This includes a Defence Maritime Patrol Aircraft, equipped with liferafts, a Customs surveillance aircraft and two
Armidale-class patrol boats - HMAS Larrakia and HMAS Wollongong. A number of other civilian vessels are also responding.
A Customs surveillance aircraft "detected a possible maritime people smuggling vessel in distress" at 3pm on Thursday.