UPDATED 6:03PM: A missing AirAsia plane carrying 162 people is likely at the bottom of the sea, Indonesia's rescue chief says.

READ MORE: AirAsia plane flying too slow: experts

Indonesia resumed its sea and aerial search at first light on Monday, but hopes have faded that survivors will be found.

National Search and Rescue chief Henry Bambang Soelistyo told a news conference the plane is most likely to have crashed into the ocean.

"Based on the co-ordinates that we know, the evaluation would be that any estimated crash position is in the sea, and that the hypothesis is the plane is at the bottom of the sea," he told a news conference.

The Airbus A320-200 disappeared en route from Surabaya in Indonesia's east Java to Singapore after the crew requested a change of flight plan due to stormy weather, in the third crisis for a Malaysian carrier this year.

Five aircraft will be sent to search for the plane, including two C-130 military transport aircraft and a Boeing 737, Indonesian air force spokesman Hadi Cahyanto said.

"Two planes have already left. Three more will follow suit. It is cloudy in some parts but still bright," Cahyanto said.

"We are focusing the search area in the waters on the eastern and northern part of Belitung island."

Australia, Malaysia and Singapore have also joined the search, which is centred on the Java Sea. The US has also said it was ready to assist.

A Royal Australian Air Force AP-3C Orion equipped with sophisticated search equipment took off on Monday from Darwin while Singapore said it was deploying two C-130 aircraft in addition to naval ships already dispatched.

AirAsia said 155 of those on board flight QZ8501 were Indonesian, with three South Koreans and one person each from Singapore, Malaysia, Britain and France. The Frenchman was the co-pilot.

Distraught relatives of the missing passengers spent the night in Surabaya hoping for news of their loved ones.

Security was tight at the airport crisis centre, with dozens of security officers and soldiers seen standing guard.

Air traffic controllers lost contact with the twin-engine aircraft around an hour after it left Surabaya's Juanda international airport at about 5:35 am local time on Saturday.

Shortly before disappearing, the pilot asked to ascend by 6,000 feet to 38,000 feet to avoid heavy clouds, according to an Indonesian transport ministry official.

The search is focused on waters around the islands of Bangka and Belitung in the Java Sea, across from Kalimantan on Borneo island, but the army has also been asked to carry out ground searches, including in mountainous areas.

AirAsia boss speaks out

AirAsia's chief executive Tony Fernandes held a press conference yesterday, in which he spoke of his concerns.

"Our concern right now is for the relatives, for the next of kin. There is nothing more important to us,” he said.

"For our crews' family and for the passengers family - that we look after them."

"We are very devastated by what's happened. It's unbelievable but we do not know what's happened yet so we will wait for the accident investigation to find out what's happened."

Fernandes, a former record industry executive, acquired the then-failing airline in 2001. It has seen spectacular success and aggressive growth under his low-cost, low-overhead model.

While its rival Malaysia Airlines faces potential collapse after two disasters this year, AirAsia confirmed this month its order of 55 A330-900neo at a list price of $15 billion.

'A country in shock'

Hope is fading for those onboard Air Asia flight 8501.

CNN's Andrew Stevens says it's a nightmare for the families waiting for some kind of news.

"The vast majority of the passengers onboard, 150 of the 155 passengers, were Indonesian so this tonight is a country in shock obviously as to what's happening...Hoping for the best but obviously at this stage fearing for the worst," he said. 

Sky's Richard Suchet says the families of those onboard face an excruciating wait.

"They can't be sure whether they've lost loved ones but they do know their is a distinct possibility. Etched in their faces is disbelief and shock," he says. 

"A seemingly endless wait for information and confirmation makes it all the more distressing."

More trouble for Malaysian aviation

The latest incident comes at the end of a disastrous year for Malaysian aviation.

Malaysia Airlines Flight MH370, carrying 239 people, disappeared in March after inexplicably diverting from its Kuala Lumpur-Beijing course. No trace of the aircraft has been found.

Just months later MH17 went down in July in rebellion-torn eastern Ukraine - believed to have been hit by a surface-to-air missile - killing all 298 aboard.