A widening search for missing AirAsia Indonesia flight QZ8501 is unlikely to locate survivors, with the head of the Indonesian rescue efforts suggesting the aircraft was likely at the bottom of the ocean.

Bambang Soelistyo revealed his hypothesis based on the co-ordinates of the Airbus A320-200 when contact with it was lost.

The search for the aircraft is continuing a day after it disappeared with 162 people on board on route to Singapore.

Questions are being raised about aviation safety in the region as the sector continues to grow rapidly.

The latest incident is being linked with the disappearance of Malaysian Airlines flight MH370 in March.

No trace of that aircraft has yet been found.

Some 30 ships and 15 aircraft are taking part in the present search.

Indonesian officials said the request from pilots to increase altitude could not be immediately approved due to traffic.

The plane then disappeared from the radar screens before the pilots gave any further response.

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 AirAsia group has previously had no fatal accidents involving its aircraft.