The blast occurred at 6:30 pm Thursday night at an industrial park in Sichuan province's Yibin city, according to a statement on the website of the local work safety administration.
China has sought to improve safety standards in its chemical manufacturing and heavy industries after a spate of industrial accidents over the years.
Authorities have begun an investigation, the news agency said.
This photo taken on July 12, 2018 shows firefighters working to put out a fire after an explosion at a chemical plant in Yibin in China's southwestern Sichuan province. Xinhua cited the Jiang'an county government as saying the fire was put out on Friday morning and the injured were in stable condition.
The Southern Metropolis News reported that a mainland business registration database showed that Hengda had been established three years ago and was listed as a chemical product manufacturer and distributor.
"My first response was that something was wrong and I went the window and saw thick smoke rising from the east".
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.
In 2015, giant chemical blasts in a container storage facility killed at least 165 people in the northern port city of Tianjin.
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