A nearby section of the arterial West-East Gas Pipeline also exploded, state-run China Central Television reported.

The Ministry of Land and Natural Resources said the landslide happened after a dump of earth and construction rubbish, as high as a 20 storey-building, collapsed. The dump was too large and the slopes to steep, making it unstable, the ministry said. 

Shenzhen landslide - in pictures

Firefighters from Shenzhen and elsewhere in Guangdong province have been sifting through rubble covering an area about the size of 14 football pitches.

If they find signs of life they place a red flag in the earth.

Bulldozers then dig down under the guidance of firefighters in the hope of finding survivors, the state-run news agency Xinhua reported. 

WATCH: Workers run as buildings come down around them amid Shenzhen landslide

Seven people have been rescued at the site so far and are not said to have life-threatening injuries.

The landslide happened at about 11.40am on Sunday.

A total of 33 buildings, including 14 factory plants, two office buildings, a canteen, three dormitory buildings and 13 small buildings were hit by the landslide, according to Xinhua. 

Fifty-nine men and 32 women were still missing as of 9am on Monday. 

Security was tight in the area on Monday with police officers and armed police stationed every five to 10 metres.

Workers and residents were barred from entering the park and their request to get back to retrieve clothes because of the cold were denied. 

The waste dump, which had offical permits to operate, had been causing concern among nearby residents for two years.

“Residents have complained about the problem for a long time, but it has not been resolved,” the owner of a drinks company told the South China Morning Post.

Workers said increasing numbers of trucks had delivered construction rubbish and the dump had looked dangerous, especially during the rainy season, but their complaints had fallen on deaf ears. 

WATCH: Buildings collapse in dramatic scenes after Shenzhen landslide

Video: A landslide hits industrial park in S China's Shenzhen, gas station exploded, buildings crunched pic.twitter.com/2jpTAUVMwG

— China Xinhua News (@XHNews) December 20, 2015

 Wang Zhenxin, a former chief engineer at the Shanghai Metro Construction Corporation, said the disaster was man-made.

“The landslide is not from a natural mountain, but a huge pile of mud,” Wang told the Post.

“When one side of the pile is overloaded and the pressure builds up, it pushes the mud on the other side and it spills over.”

Wang said such a spillover was more likely in south China, where the soil was wetter and less cohesive. Rainfall is not needed to trigger such a spill, he said.

Some people lingered near the industrial park overnight because they had heard no word from missing loved ones.

Peng Canyuan, a business owner, said he saw the landslide come like a huge wave and several people working at a tyre company were buried.

He escaped, but two of his family are missing. 

He Weiming, a 36-year-old immigrant worker from Henan province in northern China said his parents, wife, two children, sister, three nieces and nephews, plus five workers he knew were missing.

“I dialled 40 mobile numbers and none could be connected,” he was quoted by Xinhua as saying.

Another resident working in a nearby laundry said she had a narrow escape from the landslide.

“I was going out for lunch with some co-workers and all of a sudden I heard a loud noise and then I saw the mud rushing towards us. I had to run. Some of my co-workers are missing,” she said.

The Shenzhen Special Zone Daily quoted one witness as saying that three members of his employer’s family were buried by the landslide. Another witness said four of his friends were trapped.

Shenzhen deputy secretary general Li Yikang said on Sunday about 900 people fled the buildings before they collapsed. About 1,500 people were scouring the debris. 

President Xi Jinping and Premier Li Keqiang have called for all-out rescue efforts. 

Shenzhen mayor Xu Qin returned from meetings in Beijing to oversee the operation.

The central hospital in Guangming New District said it has treated nine patients aged from eight to 78.

Most suffered bone fractures escaping from the landslide. 

An eight-year-old boy was carried by his father and jumped from the seventh floor to the earth beneath when their building was struck. The father broke his leg and boy was only scratched.

The People’s Hospital in Guangming New District has treated five patients.

Among them was a young woman who has suffered a mental breakdown after her child was buried in landslide. She is receiving treament from psychiatrists, according to the Southern Metropolis News.

The Health Ministry has sent three experts in neurosurgery, intensive care and orthopedics from Beijing’s top hospitals to help with treatment in Shenzhen.

The provincial medical authorities of Guangdong have also dispatched a reinforcement group of seven senior doctors to the city, Xinhua said. 

An environmental assessment report submitted in January said the tip was on top of a quarry that had caused serious soil erosion, posing a danger to surrounding hillsides, the news website Sohu reported.

Additional reporting by Jun Mai and Liu Zhen