AirAsia Flight QZ8501 with 155 people on board -- including one British, one Malaysian, one Singaporean, three Koreans, -- and seven crew members lost contact with air traffic control at 0724 local time Indonesia (0454 IST).
Sixteen children and one infant were among the passengers on board the AirAsia Airbus A320-200 that went missing on the flight from Surabaya, Indonesia, to Singapore.
There were unconfirmed media reports that a aircraft crashed in the waters of East Belitung, off the east coast of Sumatra.
The exact location of the crash site has not been identified, media reports said.
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The aircraft was in the Indonesian Flight Information Region (FIR), more than 200 nm southeast of the Singapore -- Jakarta FIR boundary, when contact was lost, Civil Aviation Authority of Singapore (CAAS) said.
Contact with the plane was lost 42 minutes after takeoff. There were no Indian nationals on board.
A statement on AirAsia's Facebook page said: "AirAsia Indonesia regrets to confirm that flight QZ8501 from Surabaya to Singapore has lost contact with air traffic control at 0724hrs this morning."
"At the present time we unfortunately have no further information regarding the status of the passengers and crew members on board, but we will keep all parties informed as more information becomes available," the Malaysia-based carrier said in a statement.
The aircraft was an Airbus A320-200 with the registration number PK-AXC.
Indonesian Transport Ministry official Hadi Mustofa said the plane had asked for an unusual route before it lost contact, local media reported.
Air Asia said the pilot had requested "deviation" from the its flight plan because of bad weather.
"The aircraft... Was requesting deviation due to en route weather," it said.