At least 91 people were reported missing Monday, after a disastrous mudslide destroyed 33 or more buildings in the Southern Chinese city of Shenzhen.

According to the Ministry of Land and Resources, the landside was caused by the collapse of an enormous man-made pile of dirt, cement and construction waste accumulated over the course of two years.

Heavy rain in the region softened the soil, leading to the Sunday disaster.

"The pile was too big, the pile was too steep, leading to instability and collapse," the ministry said, via NBC News.

The destructive wave of red mud covered 454,000 square yards over three industrial parks. Factories, residences and various low-rise buildings were left buried in its wake.

Local authorities said 59 men and 32 women were reported missing, many believed to be buried under a sea of mud as deep as 20 feet in some areas.

The Chinese Xinhua news agency reported that 14 people were rescued in the catastrophe. 900 others were evacuated from the area Sunday.

Dr. Li, who witnessed the event, sent cellphone footage of a building collapse to NBC.

"I was on my way to the disaster site and saw a second landslide," Li said. "As you see in the video, people could escape when the second landslide happened but when the first happened, people didn't have a chance."

Many were critical of the circumstances that led to the disaster, namely the mishandling of construction debris and general lack of regard for human welfare. In 2013, The New York Times reported on the accumulation of waste created by China's frequent construction.

"Heavy rains and a collapse of a mountain are natural disasters, but this wasn't a natural disaster, this was man-made," local resident Yi Jimin said to The Associated Press.

The landslide is the fourth major disaster to happen in China this year, none due to natural causes. Previous incidents included a New Year's Day stampede in Shanghai, the capsizing of a cruise ship in the Yangtze River and a chemical plant explosion in Tianjin.