Twenty-one people have been killed in an explosion at an energy plant in the city of Dangyang in China’s central Hubei province, news website Jingchu reported Thursday.

The blast at Madian Ganshi Co. Ltd occurred at 3:20 on Thursday afternoon, and was reportedly caused by a ruptured steam pipe. Five people were reportedly injured, three of whom severely.

Liu Chun, deputy director at China Electric Power Research Institute, told Sixth Tone’s sister publication The Paper on Thursday that steam in such pipelines can reach up to 600 degrees Celsius. “When an explosion happens, the steam can fill a huge area in an instant,” Liu was quoted as saying.

People who visited the scene said the plant was in a state of disarray in an article published by state-run news agency Xinhua on Friday morning. Control room monitors were shattered, and the building was full of broken furniture.

As of Thursday, casualties had been transported to a hospital, and rescue operations at the scene were underway, reported Jingchu.

According to Jingchu, Madian Ganshi Co. Ltd, established in 2002, is an electricity and heating supplier that also produces slag, cinder, and oil-based products.

The plant where the explosion occurred burned coal gangue, a solid waste product of coal production, to generate electricity.

The Paper reported that the municipal environmental protection bureau investigated the company in 2015 for allegedly exceeding exhaust emissions. A report evaluating the environmental impact of Madian Ganshi by the provincial bureau in 2012 listed fire and explosion caused by leaks as potential hazards arising from the company’s activity, among other dangers.

This article has been updated to include additional information.

(Header image: Ruptured pipes are seen at the explosion site in Dangyang, Hubei province, Aug. 12, 2016. Xiao Yijiu/Xinhua)