JAKARTA (REUTERS) - Indonesian divers believe they are close to finding the cockpit voice recorder of a Sriwijaya Air jet that plunged into the sea shortly after take-off with 62 people on board.

Divers retrieved the plane's flight data recorder (FDR) from the seabed on Tuesday (Jan 12) and officials said they had also found the beacon that was attached to the cockpit voice recorder (CVR).

"God willing, we will find it today," said Navy official Wahyudin Arif, referring to the cockpit voice recorder.

He told KompasTV on Wednesday that divers would comb a very narrow area of the seabed for the voice recorder, adding that divers found the first black box by shifting debris on the seabed piece by piece and he suspected the same process would be needed to find the other recorder.

Military chief Hadi Tjahjanto said on Tuesday he had "high confidence" of finding the recorder soon.

The Boeing 737-500 jet crashed into the Java Sea last Saturday four minutes after take-off from Jakarta's main airport, killing all on board.

Investigators will rely heavily on the two black boxes to determine the cause of the crash.

Indonesia's National Transportation Safety Committee (KNKT) expects to download the FDR data within two to five days.

The FDR contains about 25 hours of data on eight tracks and the CVR has 30 minutes of conversation, according to the final report on a similar model of a Boeing 737 which crashed in 2008.

A team from the US National Transportation Safety Board will be travelling to Jakarta in coming days to help with the investigation.

The KNKT's initial findings showed the plane's engine was running when it hit the water, based on the damage seen on jet parts retrieved from the sea.

Indonesia's transport ministry said on Tuesday that the plane, which was grounded during the early months of the coronavirus pandemic, had passed an airworthiness inspection on Dec 14 and had returned to service shortly after.