The second black box of the crashed Chinese passenger plane has yet to be found, official media reported on Friday, retracting an earlier announcement that it has been recovered from the crash site.

The state-run China Daily had reported earlier quoting the Civil Aviation Administration of China (CAAC) that the second black box has been recovered.

However, the daily quoted a report by the state-run news agency Xinhua that the second black box had not been found.

The black box could offer vital clues about the crash in which 132 people are feared to have died.

The first black box, stated to be the Cockpit Voice Recorder (CVR) which was recovered earlier, is being decoded at a laboratory in Beijing and the data downloading and analysis work is underway, officials said.

The second black box located in the back of the plane was stated to be the flight data recorder (FDR). The flight data recorder stores information about speed, altitude and direction, as well as pilot actions and performance of important systems.

The data of the Cockpit Voice Recorder was awaited keenly as China Eastern Airlines flight MU5735 sharply dropped from an altitude of 29,100 feet to 9,075 feet in just two minutes and 15 seconds, crashing into a mountainous area.

Zhu Tao, head of the aviation safety office of the Civil Aviation Administration of China, said the possibility that the data storage unit of the cockpit voice recorder was damaged cannot be ruled out at present.

Hu Xiaobing, professor of School of Safety Science and Engineering of the Civil Aviation University of China, told state-run CGTN that this crash is very unusual for it being vertical. It seems to him, for some reason unknown yet, the pilots may have already become unconscious during the flight's steep descent.

The Boeing 737-800 plane with 132 people on board crashed on Monday in a village in Tengxian County in the city of Wuzhou. No survivors have been found so far.

China Eastern Airlines, which owned the crashed plane, and its subsidiaries temporarily grounded 223 Boeing 737-800 aircraft, and the airline has launched a sweeping safety overhaul, Liu Xiaodong, head of the airline's publicity department, told a press briefing.

All grounded aircraft are undergoing checks and maintenance according to the highest safety standards to ensure that they meet the airworthiness requirements, Liu said.

Liu added that 305 family members of 56 passengers on board the crashed plane arrived at Wuzhou by Thursday morning, with over 200 family members visiting the crash site.

On Thursday, pieces of engine wreckage from the crashed passenger plane were found.

The main impact point of the plane crash has been basically determined, Zhu said, adding that most of the plane wreckage was scattered within a radius of about 30 metres of the main impact point and the depth from the surface extends to about 20 metres underground.

So far, a total of 183 pieces of aircraft wreckage, some remains of victims and 21 pieces of belongings of victims have been found and handed over to the investigation team, Zheng Xi, head of the fire brigade of the Guangxi Zhuang Autonomous Region said.