The blast occurred at a workshop of Shandong Tianbao Chemical Industry Co Ltd in Pingyi County, Linyi City in the morning, destroying 401 workshops. The plant manufactures explosives.
All nine workers in the workshop were killed and two in a neighbouring workshop were injured, one critically.
The nine killed includes a 26-year-old women and eight men aged between 24 and 41. DNA testing is under way to confirm the bodies.
The rescue work ended with search and rescue experts confirming the nine fatalities, state-run Xinhua news agency reported.
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The company, founded in 1958, is a designated manufacturer of explosive materials for civil use.
A number of explosions in chemical factories have been reported in recent months.
In China's worst industrial accident, twin blasts destroyed a huge warehouse which stored an assortment of highly explosive chemicals in Tianjin city on August 12 in which 173 people were killed and over 700 were injured.