The second black box, believed to be the flight data recorder of the crashed Chinese passenger plane is yet to be found by the search team. 

On Thursday, hundreds of people in rain gear and rubber boots searched muddy, forested hills in southern China for the second flight recorder.

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No survivors have been found since the China Eastern Airlines Boeing 737-800 dived into a mountainous area Monday, but authorities say they still are looking.

Some human remains and engine parts were found, as well as items from the cockpit and some belongings to passengers, officials said. State TV showed searchers on a denuded slope trying to dislodge a white wing section with the airline’s red-and-blue logo.

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Earlier, one of two black box recorders, believed to be the cockpit voice recorder, was found on Wednesday. Its outer casing was damaged but the orange cylinder was relatively intact, investigators said.

The US National Transportation Safety Board said talks were ongoing with China over dispatching an expert to participate in the investigation, as is standard when the planes involved are from American manufacturers.

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“Travel to China is currently limited by visa and COVID quarantine requirements. We are working with the Department of State to address those issues with the Chinese government before any travel will be determined,” NTSB spokesperson Peter Knudson said in a statement.

China Eastern, one of China’s four major airlines, said Thursday the Shanghai-based carrier and its subsidiaries have grounded a total of 223 Boeing 737-800 aircraft while they investigate possible safety hazards.

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The plane that crashed was flying from Kunming, the capital of Yunnan province in China’s mountainous southwest, to Guangzhou, a major city and export manufacturing hub in the southeast. Authorities say there were no foreign passengers aboard.

Investigators have said it is too early to discuss possible causes. An air traffic controller tried to contact the pilots several times after seeing the plane’s altitude drop sharply but got no reply, officials have said.