An AirAsia flight traveling from the Indonesia to Singapore has lost contact with air traffic control with 162 people on board.
Flight QZ8501 lost contact at 07:24 (23:24 GMT), Malaysia-based AirAsia tweeted.
Search and rescue operations are under way.
Malaysia's national carrier Malaysia Airlines has suffered two disasters this year - flights MH370 and MH17 - but AirAsia has never lost a plane.
Flight MH370 disappeared on a flight from Kuala Lumpur to Beijing in March with 239 passengers and crew, and MH17 was shot down over Ukraine in July, killing all 298 on board.
The AirAsia flight had been due to arrive in Singapore at 08:30 (00:30GMT).
The missing jet had requested a "deviation" from the flight path due to bad weather, the company said.
There were 155 passengers on board, with 138 adults, 16 children and one infant, the company said in a statement. Also on board were two pilots and five cabin crew.
Most of those on board were Indonesian, but there were six others on board, AirAsia has said: three South Koreans, and one each from France, Malaysia and Singapore.
An official with the transport ministry, Hadi Mustofa, told local media the plane lost contact over the Java Sea, between the islands of Kalimantan and Java.
He said the plane had asked for an unusual route before it lost contact and that the weather had been cloudy.
AirAsia has set up an emergency line for family or friends of those who may be on board. The number is +622 129 850 801.
The company's chief executive, Tony Fernandes, tweeted: "Thank you for all your thoughts and prayers. We must stay strong."