A landslide that left at least 91 people missing in southern China may have started from a man-made pile of earth and construction debris, an initial government investigation showed, drawing new scrutiny to safety practices in China.

The landslide started in an area “mainly used for piling up muck and construction waste,” the Ministry of Land and Resources said in a statement on its website. The official Xinhua News Agency said the slide left 91 people missing, while a pipeline supplying natural gas to Hong Kong was also disrupted.

Satellite images of the area from 2013 and April of this year show a mound of Earth where a reservoir had once been. The ministry statement said a large amount of the heap had been piled up “too steeply.”

If the initial findings turn out to be true, they would fuel renewed concern about safety lapses made during the construction boom that’s fueled China’s economic growth. Similar scrutiny followed a deadly blast at a warehouse holding toxic material in the port city of Tianjin, as well as the 2008 earthquake in Yunnan province that killed thousands of children who were trapped in poorly built schools.

The landslide occurred in the Liuxi Industrial Park in a northwestern section of the city on Sunday. More than 30 buildings were damaged or destroyed by the landslide, the official Xinhua News Agency reported, while rescue crews were searching for those buried in the mud.

China National Petroleum Corp will start building a temporary pipeline Tuesday, a process that will take seven to 10 days, according to a statement posted on the company’s verified WeChat account.

The damaged pipeline mainly supplies the Lung Kwu Tan power plant in Tuen Mun, which has 3 million cubic meters of daily capacity and accounts for a quarter of Hong Kong’s electricity, said ICISChina, a Shanghai-based commodities researcher. PetroChina’s Beijing-based spokesman Mao Zefeng didn’t answer calls to his office and mobile phones seeking comment.

–With assistance from Fion Li.