A suspected asylum seeker boat has capsized north of Christmas Island.
The Australian Maritime Safety Authority has confirmed a search and rescue operation is underway.
Customs and Border Protection believes up to 2000 people were on board.
Other reports say survivors have been spotted.
Customs said the vessel was about 110 nautical miles (200km) north of Christmas Island in the Indonesian search and rescue region.
Indonesia’s BASARNAS was the lead authority for co-ordinating search and rescue efforts, while ASMA was organising the Australian end.
“Customs and Border Protection and Defence assets are being deployed,” Customs said in a statement.
This included a Defence aircraft equipped with life rafts, a Customs maritime surveillance aircraft, and two Armidale class patrol boats, HMAS Larrakia and HMAS Wollongong.
A number of civilian vessels are also responding.
The stricken vessel was spotted about 3pm AEST on Thursday by a Customs surveillance plane.
More than 50 asylum seekers died when a boat known as SIEV 221 crashed into rocks off Christmas Island in December 2010.
Most of the passengers were Iranian or Iraqi nationals and the youngest to die was three months old.
The disaster was the largest loss of life in Australian waters in peacetime in 115 years.
As many as 200 people drowned last December when an overloaded boat sank off the coast of East Java on its way to Australia.
Just 49 people survived the tragedy, which occurred in rough monsoonal seas on 17 December.
So far this year, 57 boats carrying a total of 4006 passengers and 82 crew have reached Australia.
For the month of June, there have been 18 arrivals, carrying a total of 1108 people.
The latest arrived overnight and had 117 people on board. – AAP