It comes amid a drive to strengthen industrial safety, with China ramping up checks over the last year, in the wake of some high-profile incidents at coal mines and chemical plants.

The cause of Thursday evening's blast at Yibin Hengda Technology in an industrial park several hours southeast of Chengdu, the capital of the southwestern province of Sichuan, is not yet known, the local government in Jiang'an county said.

The injured are in stable condition and an investigation has begun, state news agency Xinhua said.

The company, which makes chemicals for the food and pharmaceutical industries, did not immediately answer telephone calls from Reuters to seek information.

Photographs on Chinese social media showed a huge fire and plumes of smoke rising from the facility. The fire, which broke out early on Thursday evening, was put out by 11:30 p.m., the government said in its statement.

A trio of three-storey buildings was reduced to their steel frames by the explosion, the Sichuan Daily newspaper said, citing eyewitness accounts.

Windows of nearby buildings were shattered by the explosion at the factory, which is surrounded by a sand and gravel plant, it added.

The plant has three production lines, making 300 tonnes per year (tpy) of benzoic acid, which is used in food preservatives, and 2,000 tpy of 5-nitroisophthalic acid, for medicines and dyes, the regional environmental protection bureau says.

China's breakneck pace of economic growth during the last decade has resulted in a spate of industrial accidents.

In 2015, an explosion in a chemical warehouse in the northern port city of Tianjin killed 165 people. Last year a blast at a petrochemical plant in eastern Shandong province killed eight people and injured nine.