Aviation officials previously confirmed they had found a black box they believed to be the cockpit voice recorder, which should provide important clues to the cause of the crash.

The stricken jet, a Boeing 737-800, was equipped with two recorders: one in the rear passenger cabin tracking flight data, and the other a cockpit voice recorder.

Rescuers are still looking for the other recorder.

The cause has mystified aviation authorities, who have scoured the site's rugged terrain for clues as to what sparked China's deadliest plane crash in nearly 30 years.

China Eastern had earlier said the crashed plane, which was nearly seven years old, had met all airworthiness requirements pre-flight.

Following the incident, the company launched a safety overhaul, grounding all 223 of its Boeing 737-800 aeroplanes for checks.

The disaster provoked an unusually swift public response from President Xi Jinping, who ordered a probe into its cause as aviation authorities vowed an extensive two-week check-up of China's vast passenger fleet.

The safety message has rippled out across sectors.

A notice from the State Council and Ministry of Emergency Management on Wednesday called for industries across the board to "rectify potential safety hazards".

The crash affects the return for Boeing's 737 MAX in China, the last big market where the US planemaker is still awaiting approval to resume flying following crashes in Indonesia and Ethiopia that killed a combined 346 people in 2018 and 2019.