The hunt for AirAsia flight QZ8501 has begun for a third day, with the search area now expanding far beyond the plane's original flight path.

Countries around the region as well as the US, France and Australia are joining the search over the Java sea.

The Airbus A320-200, carrying 162 people, disappeared on Sunday shortly after leaving Surabaya in eastern Java on its way to Singapore.

The pilot's last contact was a request to divert around bad weather.

Indonesian officials say air traffic control approved one request, then gave clearance to a second request two to three minutes later for the plane to climb.

No reply was received from the plane, which then disappeared from radar. No trace has been found despite a two-day search.

On board the plane were 137 adult passengers, 17 children and one infant, along with two pilots and five crew.

Most were Indonesian but the passengers included one UK national, a Malaysian, a Singaporean and three South Koreans.

Pilot Capt Iriyanto had more than 20,500 flight hours, almost 7,000 of them with AirAsia. The co-pilot was French national Remi Emmanuel Plesel.

Thirty ships and planes resumed the search, with four more search areas added to existing seven patrols.

The multinational operation, led by Indonesia, has been joined by Malaysia, Singapore and Australia, with other offers for help from South Korea, China and France. The US destroyer USS Sampson is on its way to the zone.

The BBC's Alice Budisatrijo in Surabaya says the offers of foreign help come as welcome news to the relatives, who understand the limited technical capabilities of the Indonesian authorities to locate and retrieve the plane, especially if it is underwater.

Bambang Soelistyo, the head of Indonesia's search-and-rescue agency, told the Associated Press that military helicopters had been despatched to scour land over Borneo island.

"Until now, we have not yet found any signal or indication of the plane's whereabouts," he said.

On Monday, he said he suspected the aircraft was at the bottom of the sea, but there is so far no evidence of this.

The Indonesian air force said the search was seeking to establish whether an oil patch spotted off Belitung island - a busy shipping lane - was aviation fuel or from a ship.

'Then no reply'

The plane had left Surabaya in eastern Java at 05:35 on Sunday (22:35 GMT Saturday) and had been due to arrive in Singapore at 08:30.

Wisnu Darjono, AirNav safety director, said Capt Iriyanto, 53, requested permission to bank left at 06:12 to avoid a storm. The request was immediately granted and the plane changed course.

According to state navigation operator AirNav Indonesia, the pilot then asked to take the plane from 32,000ft (9,800m) to 38,000ft but did not explain why he wanted to do so.

Indonesian air traffic control staff told the pilot he could take the plane to 34,000ft but no higher because another AirAsia airliner was flying at 38,000ft.

"It took us around two to three minutes to communicate with Singapore," Mr Darjono said. "But when we informed the pilot of the approval at 06:14, we received no reply."

The plane was officially declared missing at 07:55.

It is unclear what happened next but one report suggests the plane may have tried to climb through the storm.

Former pilots say a climb could have led to reduced stability and possibly a fatal stall, as cross winds and down draughts battered the plane.

The AirAsia plane was delivered in 2008, has flown 13,600 times, completing 23,000 hours, and underwent its last maintenance in November.

AirAsia previously had no fatal accidents involving its aircraft.

Source: BBC