The search area for the second black box from a passenger jet which crashed in southern China with 132 people on board has been expanded, state broadcaster CCTV said.

It comes as intermittent rain impeded the search for a second day.

One of the black boxes, believed to be the cockpit voice recorder, was found on Wednesday.

Its outer casing was damaged but the orange cylinder inside was relatively intact, investigators said.

The China Eastern Boeing 737-800 was cruising at 29,000 feet when it suddenly nose-dived into a remote mountainous area on Monday, sparking a fire in the surrounding forest that could be seen in Nasa satellite images.

No survivors have been found.

Searchers have been using hand tools, metal detectors, drones and sniffer dogs to comb the heavily forested, steep slopes.

Wallets, identity and bank cards and human remains have been found.

CCTV news showed police in olive and dark-coloured 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 were all wearing 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 of the crash.

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.

Flight 5735 was headed from Kunming, the capital of Yunnan province, to Guangzhou, a major city and export manufacturing hub on China’s south-east coast.

China Eastern, based in Shanghai, is one of China’s four major airlines.