Rescuers have found no survivors so far from a jet carrying 132 people which crashed in hills in southern China.

Crash investigators also had no information on why China Eastern flight MU5735 plummeted out of the sky on Monday.

Recovery work at the site of the Boeing 737-800 crash in Guangxi province is being hampered by difficult terrain.

There has been an outpouring of grief in China, where families of passengers and crew are waiting for news.

Hundreds of responders have been scouring the steeply forested slopes in Wuzhou where debris from the plane was strewn after it broke apart and set fire to the hillside.

There had been no official word on casualties until China's Civil Aviation Administration held its news briefing, some 36 hours after the disaster.

"Up to now, search and rescue work has not found any survivors. Given the information currently available, we still do not have a clear assessment of the cause for the crash," Zhu Tao, aviation safety office director at the CAA, told reporters.

Air controllers had repeatedly called the aircraft during its descent but had received no response, he added.

Rescuers have so far found parts of the 737's burnt wreckage. State broadcasters showed images of the charred remains of letters, bags, wallets and identity cards belonging to those on board.

Meanwhile, the families and friends of the 123 passengers and nine crew have gathered at each end of the flight - with relatives visiting China Eastern's offices in Yunnan province and waiting at Guangzhou International Airport.

The China Eastern Airlines flight from Kunming, the capital of Yunnan, had been due to land in Guangzhou on Monday afternoon.

China Eastern has grounded all its Boeing 737-800s and set up a hotline for people seeking information on those on board.

Authorities have yet to identify passengers and crew members, but some relatives have spoken to local media or shared their grief online.

One woman reported the loss of her newly-wed husband on her WeChat account. Her earlier posts included videos of the couple's holiday trips.

Other passengers included a group of six people, one of them a teenager, who were on their way to Guangzhou to attend a funeral, a local newspaper

Another woman interviewed said her sister and close friends were part of that group, adding that she had also been booked on the flight, but ended up switching to an earlier plane.

"I feel very anguished," she told Jiemian News.

Reuters quoted a man at the airport who said he was the colleague of a passenger named Mr Tan.

After confirming that Mr Tan was on board, he had to break the news to Mr Tan's family. "They were sobbing. His mother couldn't believe this had happened. Her boy was only 29 years old," he told the news agency.

He added that arrangements were being made by the airline to bring families to the crash site in Wuzhou.

Pictures show distraught families waiting in a cordoned-off area at Guangzhou airport, being assisted by airline staff.

One unverified clip circulating widely on Chinese social media shows a man slumped in his seat crying and lamenting the loss of his three children who were on the flight. (BBC)

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