Divers are being deployed to scan the seabed for wreckage and for victims. Photo: Reuters

A French crash investigation team is using sensitive acoustic detection devices to try to locate the plane and its "black box" flight recorders.

The Airbus A320-200 was flying from Surabaya in Indonesia to Singapore with 162 people on board when it vanished.

No survivors have been found and the cause of the crash remains unknown.

More bodies were recovered on Friday, bringing the total found to 30, said officials in Pangkalan Bun, the closest town to the presumed crash site.

Four people have been identified so far.

The plane is almost certainly at the bottom of the relatively shallow Java Sea.

The head of Indonesia's search and rescue agency, Bambang Soelistyo, estimated the fuselage was at a depth of about 25-30m (80-100ft).

Several pieces of debris have been recovered, including what is thought to be part of a wing flap.

But despite a massive five-day search, the fuselage is still missing. Officials say most of the passengers could still be inside.

The BBC's Rupert Wingfield-Hayes in Pangkalan Bun says there is a growing sense among search teams that their task is going to be harder than initially thought.

Bad weather and churning seas have dashed hopes of finding the plane visually, he says, and teams will now be relying on scans of the sea floor.

The French ship, with Singaporean and Indonesian experts on board, is carrying detection equipment, including hydrophones, to listen out for the plane's two so-called black boxes - the cockpit voice recorder and the flight data recorder.

Locating the fuselage and the flight recorder will help answer the mystery of what happened to make the plane fall from the sky.

Mr Soelistyo said on Friday that wreckage and bodies were spread over a 5km area of the Java Sea.

The search has zoned in on an area of 1,575 nautical square miles of the Java Sea off Borneo, he told reporters.

"Divers are already on standby at the navy ship Banda Aceh to dive on that priority area to locate the body of the plane," he said. "I hope we'll get a significant result today."

'Unbelievably steep climb'

There were 137 adult passengers, 17 children and one infant, along with two pilots and five crew, on the plane. The majority of those on board were Indonesians.

Some investigators are reported to believe that the plane may have gone into an aerodynamic stall as the pilot climbed steeply to avoid a storm.

Officials have said the plane was travelling at 32,000ft (9,750m) when it requested to climb to 38,000ft to avoid bad weather.

When air traffic controllers consented to allow it to climb to 34,000ft a few minutes later, they got no reply.

A source quoted by Reuters said that radar data appeared to show that the aircraft's "unbelievably" steep climb may have been beyond the Airbus A320's limits.

However, the unnamed source emphasised that more information was needed before a definitive conclusion could be reached.

AirAsia previously had an excellent safety record and there were no fatal accidents involving its aircraft.