A landslide which swept through an industrial park in southern China buried more than 20 buildings in a sea of mud, left 27 people missing and triggered a gas explosion on Sunday, state media reported.

Witnesses described a mass of red earth and mud racing towards the park in the city of Shenzhen before burying or crushing homes and factories, twisting some of them into grotesque shapes.

More than 1,500 emergency workers were involved in the rescue.

In its latest update Sunday evening the official Xinhua news agency reported three injured and 27 still missing. It was unclear whether there had been any fatalities.

The slide ruptured a natural gas pipeline and triggered an explosion at the Hengtaiyu industrial park which was heard about four kilometres away, the agency said.

It said debris covered more than 10 hectares (25 acres).

About 900 people were moved out of harm's way before the landslide struck late in the morning in the city bordering Hong Kong, according to the Shenzhen Evening News newspaper.

The landslide buried 22 residential and industrial buildings including two worker dormitories, state broadcaster CCTV said. But it quoted Ren Jiguang, deputy chief of Shenzhen's public security bureau, as saying most people had been evacuated beforehand.

The cause of the slide was unclear. A video posted by Xinhua showed a massive dust cloud and piles of rubble where buildings once stood. Rescue helicopters were in operation near the scene.

"I saw red earth and mud running towards the company building," one local worker was quoted by Xinhua as saying.

"Fortunately, our building was not hit, and all people in our company were safely evacuated," the worker said, adding that a fishpond broke the full force of the landslide.

A woman surnamed Hu told the Shenzhen Evening News she saw her father buried by earth in his own truck.

"It's been hours after he was buried, and we are quite worried," she said.

President Xi Jinping and Prime Minister Li Keqiang ordered immediate rescue efforts.

The State Council, or cabinet, sent a working group to coordinate rescue efforts, which involved almost 100 fire trucks plus sniffer dogs, drones and other equipment.

A landslide last month that engulfed 27 homes in rural Zhejiang province killed 38 people.