A power plant explosion killed at least 21 people and injured five, three of them seriously, in Dangyang, Hubei province, on Thursday, according to China's top work safety watchdog.

High-pressure steam pipes at Dangyang Madian Gangue Electricity SupplyCo exploded at about 3:20 pm, killing and injuring people, the State Administration of Work Safety said in a statement.

The injured were rushed to a hospital. The cause of the blast had not yet been determined.

The power plant, an affiliate of State-owned Huaqiang Chemical Group, won approval on Jan 6 from Hubei's Development and Reform Commission to generate heat and electricity by burning coal gangue. It was licensed for power generation and sales of slag ash and petro-leum products.

Yang Huanning, head of the State Administration of Work Safety, ordered a team to be sent to the power plant to help local rescue efforts and to investigate the accident.

LiHongzhong, Party chief of Hubei, urged local officials to "do everything they can" in the search for and rescue of survivors and to prevent any secondary accidents.

Li vowed to set up an investigative team to find out what led to the accident. He ordered a province wide work safety inspection to prevent similar accidents.

From January to July, 28,115 work safety accidents occurred in China, leaving 16,059 people dead or missing, the State Administration of Work Safety said on Wednesday.

The administration warned that the risk of blasts in coal mines and mineral companies is higher in the summer.

Zhou Lihua in Wuhan contributed to this story.