Indonesian search teams believe they have found the fuselage of AirAsia flight QZ8501 in the Java Sea and hope calmer waters will allow divers to retrieve the black box flight recorders.

The jet lost contact with air traffic control in bad weather on December 28, less than halfway into a two-hour flight from the Indonesian city of Surabaya to Singapore.

None of the 162 people on the aircraft survived.

Three vessels involved in the search have detected pings about four kilometres from where the plane's tail was raised on Saturday in water about 30 metres deep.

"The navy divers in Jadayat state boat have succeeded in finding a very important instrument, the black box of AirAsia QZ8501," senior ministry official Tonny Budiono said.

"The black boxes are in a crushed part of the aircraft debris, making it very difficult for the team of divers.

"Because of time constraints, [we] have decided to retrieve the black boxes tomorrow morning by gradually shifting these layers of aircraft body debris."

If that fails, Mr Budiono said divers would lift the debris using inflatable balloons, the same technique used to lift the tail section.

However, Navy spokesman Manahan Simorangkir denied the black box had been found, saying divers could not confirm its exact location due to poor weather and visibility.

Supriyadi, operations coordinator for the National Search and Rescue Agency, said a sonar scan had revealed an object measuring 10 metres by 4 metres by 2.5 metres on the sea floor.

"They suspect it is the body of the plane," Supriyadi told reporters in the town of Pangkalan Bun, the base for the search effort on Borneo.

"If it is the body of the plane then we will first evacuate the victims."

Forty-eight bodies have been found in the Java Sea off Borneo and searchers believe more will be found in the plane's fuselage.

Strong winds, currents and high waves have been hampering efforts to reach other large pieces of suspected wreckage detected by sonar on the sea floor.

If and when the recorders are retrieved and taken to Jakarta for analysis, it could take up to two weeks to download data, investigators said, although the information could be accessed in as little as two days if the devices were not badly damaged.

While the cause of the crash was not known, the national weather bureau said seasonal storms were likely to be a factor.

President Joko Widodo said the crash exposed widespread problems in the management of air transportation in Indonesia.

Reuters/AFP