WUZHOU, China (AP) — Hundreds of searchers wearing rubber boots and full rain gear headed into muddy, forested hills in southern China on Thursday to try to find the second black box from a China Eastern passenger jet that crashed in southern China with 132 people on board earlier this week.

Three days after the crash, officials said they had found 183 pieces of the plane, including engine parts and cockpit items, 21 objects belonging to victims and some human remains. State broadcaster CCTV showed footage of workers on a denuded slope trying to dislodge a white wing section with the red and blue China Eastern logo on it.

One of the black boxes, believed to be the cockpit voice recorder, had been found Wednesday. Its outer casing was damaged, but the orange cylinder was relatively intact, investigators said.

Pumps were being used to drain a water pond as an off-and-on light rain hampered the search effort for a second straight day. More than 300 searchers were taking part, said Huang Shangwu, a deputy chief in the Guangxi Fire and Rescue Department.

“The water pumping yesterday greatly contributed to the finding of the black box,” Huang told reporters at a command center inside a wide, restricted zone that authorities have blocked off.

The Boeing 737-800 was cruising at 29,000 feet when it suddenly nose-dived into a remote mountainous area on Monday, setting off a fire in the surrounding forest that could be seen in NASA satellite images. No survivors have been found.

Foreign media were escorted into the zone for the first time Thursday. Parked police and other vehicles lined the highway into the area, and the journalists were driven down small puddled roads covered in red-brown mud to the command center.

When they passed a woman in tears who was being walked away, security officials used open umbrellas to try to block the journalists from filming from their vehicles.

Searchers have been using hand tools, metal detectors, drones and sniffer dogs to comb the heavily forested and steep slopes. Wallets, identity and bank cards and human remains have been found.

CCTV news showed police in olive- and dark-colored rain gear standing in a cleared area on Thursday, some with bare or white-gloved hands atop long-handled tools that appear to be shovels or sickles. They all wore surgical masks.

Recovering the so-called black boxes — they are usually painted orange for visibility — is considered key to figuring out what caused the crash.

Cockpit voice recorders can capture voices, audio alerts and background sounds from the engine or even switches being moved. The flight data recorder stores information about the plane’s airspeed, altitude and direction up or down, as well as pilot actions and the performance of important systems.

Investigators have said it is too early to speculate on the cause. 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.

The China Eastern flight was headed from Kunming, the capital of Yunnan province, to Guangzhou, a major city and export manufacturing hub on China’s southeastern coast. China Eastern, headquartered in Shanghai, is one of China’s four major airlines.