International search planes and ships scouring Indonesian waters for a missing AirAsia plane are focusing on a patch of oil as a top official warns the aircraft is probably at the bottom of the sea.

Australia, Singapore and Malaysia joined the Indonesia-led search as anguished relatives waited for news of their loved ones more than a day after Flight QZ8501 disappeared over the Java Sea with 162 people on board.

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

Indonesian Air Force spokesman Hadi Tjahjanto told AFP the search was now concentrated on an oil patch spotted off Belitung island in the Java Sea, across from Kalimantan on Borneo island.

"We are making sure whether it was avtur (aviation fuel) from the AirAsia plane or from a vessel because that location is a shipping line," he said.

Indonesian Vice President Jusuf Kalla said an object spotted at sea earlier was not from the plane.

"The government will not give up and is not giving a time limit for the search. What is important is to find the victims and the plane," he said.

The National Search and Rescue Agency chief Bambang Soelistyo said earlier it was likely the plane was at the "bottom of the sea".

Distraught relatives spent the night in Surabaya hoping for news as the international search expanded.

Intan, 28, said Indonesia needed overseas help to find the plane that was carrying her brother and his family and friends.

"My hope is Indonesia seeks as much help as possible from other countries. Don't claim 'We have sophisticated technology', just ask other countries because they are better equipped," she told AFP, as Jakarta welcomed offers of help from its neighbours.

"My prayer is I really, really hope that there will be news about the people on board. Whatever it is, what is important is we know where they are now," she said.

While the international operation has drawn comparisons with the ongoing search for Malaysia Airlines MH370, Prime Minister Tony Abbot said there was nothing mysterious or sinister about the latest incident.

"It's an aircraft that was flying a regular route on a regular schedule, it struck what appears to have been horrific weather, and it's down. But this is not a mystery like the MH370 disappearance and it's not an atrocity like the MH17 shooting down," he told Sydney radio station 2GB.

One Indonesian family of 10 had a miraculous escape when they arrived too late to catch Flight QZ8501.

A RAAF Orion search and communications aircraft. (9NEWS) (9NEWS)

This map shows potential search areas for missing flight QZ8501.

"Maybe it is all God's plan that my family and I were not on the flight. It was a blessing in disguise," said Christianawati, 36.

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

The missing plane was operated by AirAsia Indonesia, a unit of Malaysian-based AirAsia which dominates Southeast Asia's booming low-cost airline market.

The plane's disappearance comes at the end of a disastrous year for Malaysian aviation.

Malaysia Airlines Flight MH370 disappeared while flying from Kuala Lumpur to Beijing in March with 239 passengers and crew, and in July flight MH17 was shot down over troubled Ukraine killing all 298 on board.

An AirAsia jet.

Family members of passengers of missing Malaysian air carrier AirAsia flight QZ8501 arrive at Juanda international airport in Surabaya. (Getty Images) (Getty)