The blast occurred at the Youdao Chemical plant at around 11:57 am (0357 GMT) in Gaomi, a town in Shandong province around 450 kilometres (280 miles) southeast of the capital Beijing, according to the China News agency.
Videos broadcast by the Beijing newspaper Xinjingbao showed a gigantic column of grey smoke rising into the sky, a fire in an industrial zone and shop windows apparently blown out by the explosion.
Clips also showed debris strewn across a road, a car with a smashed windscreen, and dark orange flames devouring installations in the background.
Emergency services dispatched 55 vehicles and 232 first responders to the scene, the national Ministry of Emergency Management said in a statement.
Youdao Chemical manufactures "low-toxicity" pesticides and employs around 300 people on a site of 47 hectares (116 acres), according to the Chinese online media The Paper.
Industrial accidents occur regularly in China, where safety standards in its countless factories are sometimes not respected.
In 2015, explosions at warehouses containing flammable chemicals in the port city of Tianjin killed over 170 people and injured 700 others.
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