Authorities monitor progress in the search for AirAsia Flight QZ8501 in the Mission Control Center inside the National Search and Rescue Agency in Jakarta December 29, 2014.[Photo/Agencies]

JAKARTA - A missing AirAsia jet carrying 162 people could be at the bottom of the sea after it was presumed to have crashed off the Indonesian coast, an official said on Monday, as countries around Asia sent ships and planes to help in the search effort.

The Indonesia AirAsia plane, an Airbus A320-200, disappeared after its pilot failed to get permission to fly higher to avoid bad weather during a flight from the Indonesian city of Surabaya to Singapore on Sunday.

Flight QZ8501 did not issue a distress signal and disappeared over the Java Sea five minutes after requesting the change of course, which was refused because of heavy air traffic, officials said.

"Based on our coordinates, we expect it is in the sea, so for now (we think) it is on the sea floor," Soelistyo, head of Indonesia's search and rescue agency, told reporters when asked about the missing plane's likely location.

A senior Indonesian civil aviation source told Reuters that authorities had the flight's radar data and were waiting for search and rescue teams to find debris before they started their investigation into the cause.

Air force spokesman Hadi Tjahjanto said searchers were checking a report of an oil slick off the east coast of Belitung island, near where the plane lost contact. He also said searchers had picked up an emergency locator signal off the south of Borneo island but had been unable to pinpoint it.

On board Flight QZ8501 were 155 Indonesians, three South Koreans, and one person each from Singapore, Malaysia and Britain. The co-pilot was French.

The disappearance caps a disastrous year for Malaysia-affiliated airlines, with Indonesia AirAsia 49 percent owned by Malaysia-based budget carrier AirAsia.

Malaysia Airlines Flight MH370 went missing on March 8 on a trip from Kuala Lumpur to Beijing with 239 passengers and crew and has not been found. On July 17, the same airline's Flight MH17 was shot down over Ukraine, killing all 298 people on board.

The AirAsia group, including affiliates in Thailand, the Philippines and India, had not suffered a crash since its Malaysian budget operations began in 2002. The group's shares in Kuala Lumpur were down 8 percent at 0813 GMT.

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