At least 27 people are missing after a massive landslide hit an industrial park in Shenzhen, causing hundreds to flee as tonnes of earth buried factories and buildings.
China's West-East natural gas pipeline also exploded near the site of the disaster, the official Xinhua news agency reported.
Some 1,500 rescue personnel were deployed to Liuxi Industrial Park in Guangming New District, which has a population of 110,000.
Two workers' dormitories were among the 22 buildings engulfed and toppled over by a rush of mud and earth that an eyewitness likened to "an earthquake".
The landslide covered an area of more than 100,000 sq m - at least 14 football fields - with soil, the authorities said.
Pictures in news reports showed buildings leaning on their sides, trucks crushed and helicopters flying overhead to survey the scene.
Chinese President Xi Jinping told rescuers to save those trapped and to help the families of the injured, while Premier Li Keqiang ordered a probe into the cause of the disaster.
Chinese news reports said residents and workers first noticed the soil loosening in the hill behind their buildings in the morning, prompting many to evacuate.
As the mud took about 30 minutes to flow down the hill, 900 people escaped to safety, Xinhua said.
"(The buildings) have all collapsed, really, they have all collapsed," an eyewitness was heard saying in a 48-second video of the incident. "Run, quick, run."
Video footage showed buildings toppling over, churning up heaps of dust as they were hit by mounds of earth a few metres high.
"It was like an earthquake. The landslide hit the industrial park below directly and buried the buildings immediately," a resident was quoted as saying by Beijing News. "I met someone who jumped from the second floor to escape."
At press time, there were no confirmed casualties. Rescuers pulled out four people, three of whom sustained light injuries.
Among those still trapped were three children aged four to nine, who were at home with their grandfather, Shenzhen Evening News reported. Their parents rushed home only to find their home buried by earth.
A resident told the Beijing Youth Daily that soil from construction sites had piled up against a hill after being dumped there for the past two years.
The Shenzhen Special Zone Daily quoted an employee at the Guangming New District's safety inspection department as saying that the landslide was caused by a spillover of mud at the illegal soil dump.