The blast occurred in a workshop of Shandong Tianbao Chemical Industry Co Ltd in Pingyi County, Linyi City in the morning.
All nine workers in the workshop are unaccounted for and two in a neighbouring workshop were injured, one critically.
The nine missing includes a 26-year-old women and eight men aged between 24 and 41. The cause of the blast is under investigation.
The company, founded in 1958, is a designated manufacturer of explosive materials for civil use.
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.