One of the two black boxes of the China Eastern Airlines plane that crashed on Monday has been found, rescuers said on Wednesday.

The China Eastern Airlines Boeing 737 aircraft, which departed from Kunming and was bound for Guangzhou on Monday, crashed into a mountainous area near Molang Village in Tengxian County in the city of Wuzhou, in the worst air disaster in over a decade in the country.

A black box of the China Eastern Airlines passenger plane has been recovered, rescuers at the site told state-run Xinhua news agency.

The crashed airliner had two black boxes, one in the cockpit and one in the tail to record various data, according to the official media here.

The search for the black boxes is one of the key tasks required by the investigation team.

Aircraft black boxes are generally in bright orange-red so they can be found quickly after a flight accident. They are built to withstand explosions, disintegration, high temperature combustion, immersion in water and other damage, and the battery lasts for about 30 days.

Because the crash site is in a forested mountainous area, searchers are relying on drones and manpower, which will bring certain difficulties.

No survivors have been found so far among the 123 passengers and nine crew members in the plane crash, Sun Shiying, chairman of China Eastern Airlines Yunnan branch, said on Tuesday night.

The cause of the crash cannot be confirmed immediately and the investigation into the cause is difficult, said Zhu Tao, an official with the Civil Aviation Administration of China (CAAC) said on Tuesday.

At present, the investigation team is carrying out a full probe in accordance with the procedures, with rescuers exploring the crash site and going all out to search the black boxes, Zhu had said.

The team is also thoroughly investigating other aspects, including flight, maintenance, air traffic control, meteorology, aircraft design and manufacturing, Zhu said.

Based on known information, the authorities do not yet have a clear clue to the cause of the passenger plane crash, the official said.

The last domestic fatal incident was in 2010, when a plane crashed in Yichun, Heilongjiang province, killing 42 people.