WUZHOU: Search and rescue work in the wake of the China Eastern Airlines 600115.SS crash entered its fourth day as storm clouds retreated with efforts focusing on retrieving the second black box while the first was being decoded and analysed in Beijing.

Emergency workers on the ground have been scouring the forest-clad mountains of China's southern Guangxi region for victims of Flight MU5735 that crashed on Monday. No survivors have been found so far in a tragedy that has shocked the nation.

The jet was en route from the southwestern city of Kunming to Guangzhou on the coast when it plummeted from cruising altitude at about the time when it should have started its descent to its destination.

Rescuers recovered one of the two black boxes on Wednesday. The device, the plane's cockpit voice recorder, has been sent to Beijing. It could take 10 to 15 days to arrive at a preliminary analysis, and longer before a final conclusion can be presented in a report, according to Chinese state media.

"Our work priority is still on search and rescue," said Zhu Tao, head of aviation safety at the Civil Aviation Administration of China (CAAC), on Thursday.

The investigation is being led by China but the United States was invited to take part because the Boeing 737-800 was designed and manufactured there.

"When we enter the accident investigation stage, we will invite relevant parties to participate in the accident investigation according to relevant regulations," Zhu said.

U.S. Transportation Secretary Pete Buttigieg said Wednesday that Chinese authorities had invited the U.S. National Transportation Safety Board (NTSB) to take part in the investigation, adding that he was very encouraged by the invitation to be on the ground in China. 

The NTSB, however, later said it had not yet determined if investigators would travel to China in light of visa and quarantine requirements. 


DISTRAUGHT

More than 200 distraught family members of the 132 people on board the doomed flight have since visited the crash site.

Debris from the jetliner including engine blades, horizontal tail stabilisers and other wing remnants was concentrated within 30 metres (90 feet) of the main impact point, which was 20 metres (60 feet) deep.

A 1.3 metre-long fragment suspected to be from the plane was found about 10 km (six miles) away, prompting a significant expansion of the search area.

Some human remains and personal belongings of the passengers have also been found.

As rainy weather retreated on Friday, emergency workers renewed their search for the victims and the flight data recorder.

According to flight tracking website FlightRadar24, the plane briefly appeared to pull out of its nosedive, before plunging again into a heavily forested slope in Guangxi.

Authorities said the pilots did not respond to repeated calls from air traffic controllers during the rapid descent.

It was too early to determine the cause of the crash, which experts say are usually the result of a combination of factors.