Indonesian authorities say the black box flight data recorder of crashed AirAsia flight QZ8501 has been retrieved by divers.

The cockpit voice recorder, the second piece of the black box, has also been located, 20 metres from the flight data recorder.

The data recorder was found beneath a piece of the submerged plane's wing and was loaded onto a ship.

The equipment is being transported to Jakarta for investigation, which could shed light on how and why the plane went down.

The latest finding is a key breakthrough in Indonesia's efforts following the crash of the Airbus A320-200 on 28 December with 162 people aboard.

"At 07:11 [local time], we succeeded in lifting the part of the black box known as the flight data recorder," Fransiskus Bambang Soelistyo, the chief of Indonesia's National Search and Rescue Agency, told reporters.

"All the ships, including the ships from our friends, will be deployed with the main task of searching for bodies that are still or suspected to still be trapped underwater."

Authorities previously said the divers were struggling to retrieve the instrument as it was lodged under heavy wreckage at a depth of about 30 metres.

The condition of the recorders is still unclear.

Speaking of the analysis of the data from the black box to determine the cause of the crash, key investigator with the National Transportation Safety Committee Madjono Siswosuwarno told Reuters:

"The [data] download is easy, probably one day. But the reading is more difficult ... [it] could take two weeks to one month."