A manmade mountain of dirt and industrial waste crashed into buildings in Shenzen, China after heavy rains soaked the ground. (Storyful News)

A massive landslide has left at least 91 people missing on Monday in the southern Chinese city of Shenzhen, and is being blamed on a pile of construction waste that has built up for over two years. No deaths have been reported, though few people trapped by the slide had been rescued alive by Monday afternoon.

The liquefied red mud and debris overtook 33 buildings in an industrial park around Noon on Sunday. Videos show buildings crumbling to the ground as the landslide rakes through them. Geysers of debris exploded into the air as the mud swept through the city.

When it was all over, mud as deep as 33 feet covered an area of 450,000 square yards, authorities reported. That’s approximately 70 football fields.

The AP reports that the slide was caused by the combination of a large, man-made pile of construction waste and rain:

The Ministry of Land and Resources said the debris originated with a steep, man-made mountain of dirt, cement chunks and other construction waste that had been piled up against a 330-foot-high hill over the past two years.

Heavy rains in the region had saturated the soil, making it increasingly unstable and ultimately causing it to collapse with massive force.

“The pile was too big, the pile was too steep, leading to instability and collapse,” the ministry said, adding that the original, natural hill remained intact.

[China’s year of man-made disasters]

The landslide is the fourth deadly incident in China where human error has been blamed, the AP reports, in addition to the dangerously high levels of air pollution that has plagued Beijing for over a month:

The landslide is the fourth major disaster to strike China this year following a deadly New Year’s Day stampede in Shanghai, the capsizing of a cruise ship in the Yangtze River and a massive explosion at a chemicals warehouse in Tianjian on the coast near Beijing.

Human error has been suspected or confirmed in all three previous disasters, pointing to an often callous attitude toward safety in China despite the threat of harsh penalties.

Three decades of headlong economic growth have been catching up with China in terms of safety and damage to the environment. Many of the country’s major cities suffer from chronic air pollution. A four-day smog red alert continued in Beijing on Monday, forcing schools to close, factories to curtail production and half the city’s cars off the roads.