One of two black boxes from the crashed China Eastern airliner was recovered on Wednesday (Mar 23) as investigators try to piece together what made a jet carrying 132 passengers nosedive into a mountainside in southern China.

The cause of the disaster has mystified aviation authorities who have scoured rugged terrain for clues, finding no survivors from what is almost certain to be China's deadliest plane crash in nearly 30 years.

China's aviation authority said that the device is a cockpit voice recorder, according to an early assessment.

The data storage units in the black box are relatively complete despite some damage, Zhu Tao, an official with the Civil Aviation Administration of China (CAAC), told a media briefing.

The black box is being sent to Beijing, Zhu said.

State TV showed rescuers recovering the bright orange box and placing it in a clear plastic bag.

Flight MU5735 was en route from the southwestern city of Kunming to Guangzhou on the coast on Monday when the Boeing 737-800 jet suddenly plunged from cruising altitude at about the time when it should have started its descent ahead of landing.

Most of the jet appears to have disintegrated upon impact and no survivors have been found.