Photos circulating on social media showed plumes of smoke coming out from the remains of the building.
The accident follows previous high-profile disasters at chemical plants in China.
The blast occurred at 6:30pm Thursday at an industrial park in Sichuan province's Yibin city, according to a statement on the website of the local work safety administration.
Authorities have begun an investigation, the news agency said.
Lax regulations in China's industrial and chemical sectors have been blamed for several industrial accidents in recent years.
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Fire crews sent to the scene put out the fire later on Thursday and local firefighters told The Beijing News that the blast had been caused by exploding methanol but did not provide further details.
The company that owns the building where the fire occurred is a chemical manufacturer named Hengda, according to the official Xinhua news service.
A trio of three-story buildings was reduced to their steel frames by the explosion, the Sichuan Daily newspaper said, citing eyewitness accounts.
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.
Last year, a blast at a petrochemical plant in eastern Shandong province killed eight people and injured nine.