A man-made pile of construction waste and trash collapsed on buildings in an industrial park in Shenzhen, a city in Guangdong province.
The state-run Xinhua news agency reported the body of one victim had been found, and that more than 80 people were missing.
At least 16 people were still hospitalized, three in serious condition, according to Shenzhen's emergency response office.
The rescue effort included members of the armed forces and search dogs, Xinhua said. Doctors were also dispatched to help.
Video from the scene showed rescue workers, wearing orange clothes and hardhats, using heavy machinery and their hands to clear debris. Officials set up a rescue command center and three treatment shelters on site.
Police received a report of the landslide Sunday morning.
The company in charge of the waste dump's construction purportedly raised safety concerns in a January report filed with the municipal government.
"With the fast economic development of Guangming New District, acceleration of urbanization, and increase of municipal and property development projects, large amount of soil waste is destined to be produced. About one million square meters of soil waste is left every year in Guangming New District and there's need to find its way-out. Therefore it is needed urgently to build new waste dumps," the report read, according to the state-run Legal Evening News.
The report also brought up the issue of soil erosion, as the dump used to be a quarry, the newspaper said.
The landslide covered an area of 380,000 square meters, Xinhua reported. It resulted in a ruptured gas pipeline.
Locals told Xinhua that hundreds of trucks carrying construction waste used to dump trash into the pile every day.
A security guard working in a factory in the area told Xinhua that a 250-yuan ($38) fee was charged per truck.
He Weiming, a migrant worker from Henan province, told state media that many of his relatives were buried in the debris.
"My father, mother, son, daughter, wife, sister and her child, sister-in-law and her three children and other five workers were all in there," he said.
"I've made more than 40 calls; none of them got through. At first they didn't go through, and now the phones are powered off. When my brother and I left home in the morning, everything was fine. But when we got back around 11:40 a.m., our house had been buried. You couldn't even see the top of the once 4-meter-high building."