Indonesian navy divers prepare operations to lift the tail of AirAsia flight QZ8501 from the Java Sea on Friday. The tail section could contain the flight data and cockpit voice recorders.

AFP/Jakarta

Signals believed to be from the black box data recorders of crashed AirAsia Flight 8501 were detected on Friday, Indonesian authorities said, offering the strongest lead to explain the disaster.

However more of the bad weather that has plagued the 13-day search for the doomed plane stopped divers from quickly tracking the ping signals to the black boxes, and frustrated efforts to lift the plane's tail from the floor of the Java Sea.

"A ship detected the pings. The divers are trying to reach it," said S B Supriyadi, a director with the National Search and Agency who is stationed at search headquarters in the town of Pangkalan Bun on Borneo island.

"The location of the ping is reported to be near where the tail was found."

The plane crashed on December 28 during stormy weather as it flew from the Indonesian city of Surabaya to Singapore, claiming the lives of all 162 people on board.

Rough seas and strong currents have slowed multinational efforts to find the wreckage of the plane, which is lying in relatively shallow waters, and determine why it crashed.

The black boxes are regarded as crucial to explaining the cause of the disaster, as they should contain recordings of the pilots' final words and general flight data.

They are designed to give a ping signal for 30 days after a crash so that the recorders can be found.

The tail of the plane, where the black boxes were housed, was discovered on Wednesday partially buried in the seabed 30 metres underwater.

But no pings were initially detected.

Divers battle currents

Search officials have since Wednesday focused their efforts on and around the tail, believing the black boxes should be there unless they were dislodged.

Dozens of elite Indonesian Marine divers have tried but failed to thoroughly search the tail, in a task complicated by powerful currents and the fact it is partially buried in the seabed.

Those problems continued throughout Friday, with efforts to lift the tail using floatation devices scuppered by rough seas.

"We have tried (to lift the tail) but it was unsuccessful. We are still trying," Supriyadi said.

"The team there said the visibility was only one metre and they couldn't see. The current and waves were getting stronger so they couldn't work effectively."

Indonesian authorities have also brought a crane to the KRI Banda Aceh Navy vessel stationed close to the tail site, in hopes of using that to lift the wreckage.

American, Russian and other foreign naval ships are also involved in the hunt for other parts of the plane's wreckage, as well as for the bodies of passengers. Just 48 bodies have been found so far, according to Indonesian authorities.

All but seven of those on board were Indonesian. The non-Indonesians were three South Koreans, one Singaporean, one Malaysian, one Briton and a Frenchman - co-pilot Remi Plesel.

Supriyadi said another object was found on Friday that could be the nose of the plane, however searchers had yet to reach it to confirm.

"The shape of the object looked like the nose of a plane... we have deployed an ROV (remotely operated vehicle) but the visibility wasn't very good, we are trying to send divers."