The search is continuing for AirAsia Indonesia flight QZ8501, a day after it went missing with 162 people on board.
The head of Indonesia’s search-and-rescue agency has suggested the plane could be at the bottom of the sea, but no trace of it has yet been found.
Officials in Surabaya, from where the plane took off, said search teams were only just reaching the area of the Java Sea where the plane is believed to be.
The Airbus A320-200 disappeared early on Sunday on a flight to Singapore.
The pilots had requested a course change because of bad weather but did not send any distress call before the plane disappeared from radar screens.
“Based on the co-ordinates given to us and evaluation that the estimated crash position is in the sea, the hypothesis is the plane is at the bottom of the sea,” Bambang Soelistyo, the head of Indonesia’s search and rescue agency, told a news conference in Jakarta.
The search for the plane, near Belitung island, was largely suspended as night fell on Sunday.
Although some ships continued the hunt overnight, the main search planes and vessels, from several nations, only resumed on Monday.
Mr Soelistyo said Indonesia was providing 12 ships, three helicopters and five military aircraft.
Malaysia was to deploy a C-130 plane, along with three ships, with Singapore lending a C-130 and Australia also providing help.
AirAsia’s share price fell 7% in morning trading on Monday in Kuala Lumpur.
Flight QZ8501 had left Surabaya in eastern Java at 05:35 on Sunday (22:35 GMT Saturday) and was due to arrive in Singapore at 08:30 (00:30 GMT).
The pilot radioed at 06:24 local time asking permission to climb to 38,000ft (11,000m) to avoid the dense storm clouds.
Indonesian officials said the request could not be immediately approved due to traffic, but the plane disappeared from the radar screens before the pilots gave any further response.
AirAsia boss Tony Fernandes said this was his “worst nightmare”.
Mr Fernandes flew to Surabaya and later said: “We are very devastated by what’s happened, it’s unbelievable.
“Our concern right now is for the relatives and for the next of kin – there is nothing more important to us, for our crew’s family, and for the passengers’ families.”
Oceanographer Simon Boxall told the BBC the plane should not be too difficult to find if it went into the water.
The sea floor is within diver depth, he says, and it would be “likely that they’ll get answers within a few days”.
The AirAsia Indonesia plane was delivered in 2008, has flown 13,600 times, completing 23,000 hours, and underwent its last maintenance in November.
The captain, Iriyanto, had more than 20,500 flight hours, almost 7,000 of them with AirAsia, Mr Fernandes said. The co-pilot is French national Remi Emmanuel Plesel.
The AirAsia group has previously had no fatal accidents involving its aircraft. The airline has set up an emergency line for family or friends of those who may be on board. The number is +622 129 850 801.
Special centres were set up at both Singapore’s Changi airport and Juanda international airport in Surabaya.
There were 155 passengers on board, the company said in a statement:
• 137 adults, 17 children and one infant
• Most were Indonesian but also one UK national, a Malaysian, a Singaporean and three South Koreans
• The BBC understands that the British national is Chi-Man Choi
• Two pilots and five crew were also on board – one French, the others Indonesian
This has been a difficult year for aviation in Asia – Malaysia’s national carrier Malaysia Airlines has suffered two losses – flights MH370 and MH17.
Flight MH370 disappeared on a flight from Kuala Lumpur to Beijing in March with 239 passengers and crew. The wreckage, thought to be in the southern Indian Ocean, has still not been located.
MH17 was shot down over Ukraine in July, killing all 298 on board.
What is the AirAsia Group?
• Low-cost airline group with main hub in Kuala Lumpur, Malaysia. Founded in 2001
• AirAsia Group services now comprises eight affiliates, including AirAsia Indonesia
• Group employs more than 15,000 staff
• Operates fleet of more than 150 Airbus A320 aircraft with 200 more on order
• Flies to about 100 destinations in some 15 countries. Carried almost 8 million passengers in 2013
• Tony Fernandes has been the group’s CEO since December 2001
– BBC News