Indonesian divers have pulled out the cockpit voice recorder from the sunken wreckage of an AirAsia passenger jet, a key step towards determining the cause of the crash that killed all 162 people aboard.

The cockpit voice recorder, which retains the last two hours of conversation between the pilots and air traffic controllers, was found close to where the flight data recorder was recovered from the bottom of the Java Sea on Monday.

"Today we have completed searching for the main things that we have been looking for," Rear Admiral Widodo, the commander of the navy's western fleet, told reporters after handing over the cockpit voice recorder to investigators on Tuesday.

"But the team will still try to find the body of the plane in case there are still bodies inside."

Together the black boxes, which are actually orange, contain a wealth of data that will be crucial for investigators piecing together the sequence of events that led to the Airbus A320-200 plunging into the sea.

Al Jazeera's Step Vaessen, reporting from Jakarta, said the voice recorder was found 20m from where the flight data recorder was located and will be sent to the Indonesian capital to be analysed.

"First they have to download all the data and then analyse. There is a lot of information on these instruments. On the voice recorder there are around two hours of conversations. It will probably take a couple of months before we really know what had happened," Vaessen said.

The Airbus A320-200 airliner lost contact with air traffic control in bad weather conditions on December 28, less than halfway into a two-hour flight from Indonesia's second-biggest city of Surabaya to Singapore.

The Indonesian meteorological agency has said that stormy weather likely caused the crash, but a definitive answer is impossible without the black box, which should contain the pilots' final words as well as various flight data.

Source: Al Jazeera and agencies