The missing AirAsia Indonesia flight QZ8501 is likely to be at the bottom of the sea, BBC quoted the head of Indonesia's search-and-rescue agency reported.
Bambang Soelistyo said the hypothesis was based on the co-ordinates of the plane when contact with it was lost.
The search is continuing for the aircraft, a day after it disappeared with 162 people on board, but no trace has been found so far.
Indonesia air force spokesman Hadi Tjahnanto said the search was being focused on an area where an oil spill had been spotted but it was not clear if it had been caused by the plane.