Australian air crash investigators have assisted Indonesian authorities in retrieving some 69 hours of valuable data from a back box recorder off the Lion Air jet that crashed into the Java Sea last week.

Nurcahyo Utomo, head of the Indonesian transport safety committee’s investigation into the crash, said experts – including those from Australia, the US and Singapore – had retrieved data from 19 flights carried out by the Boeing 737 aircraft, including the JT610 flight that crashed into waters off Karawang, West Java.

The last recorded data was from October 29 at 6.31am Western Indonesia Time, Mr Utomo told a press conference on late Sunday.

The Lion Air plane took off from Jakarta’s Soekarno Hatta airport at 6.20am and lost contact with air traffic control about 13 minutes later as it crashed into the sea off Tanjung Karawang, about 70 kilometres east of Jakarta. All 189 people on board were killed.

Mr Utomo said search and rescue divers were still searching for the second black box, which contains the voice cockpit recording.

He said a strong signal from the second black box was detected on Saturday but divers were unable to locate it, possibly because it was buried in mud.

The national search and rescue agency Basarnas has so far handed over 105 body bags containing human body parts retrieved from the search area.

However police forensic teams have only been able to identify 14 bodies.

Head of Basarnas Muhammad Syaugi told a press conference on Sunday that the agency has extended the search operation by three days as divers continue to search for more remains and the plane’s main fuselage.

So far, the operation has only managed to collect parts broken off from the aircraft’s main body, including the front and back tyres and two turbines.

“Hopefully with increased synergy between the police, the military and the search and rescue agency, we can soon conclude the search operation,” Mr Syaugi said.

The operation will use remotely operated underwater vehicles.

-with AAP