Chinese state broadcaster CCTV said some chemicals were still burning by Wednesday morning, and rescuers were waiting for them to be put out before looking for the missing people.
"With explosions continuing and a fire raging, it is quite treacherous for rescuers, since there are huge hidden dangers amid the blasts, along with leaks of toxic gases such as ammonia and formaldehyde," Ma Dewen, the firefighter in charge of the rescue efforts, was quoted by Xinhua as saying.
The plant is in a development zone on the outskirts of Yizhou city and mainly produces chemicals for adhesives and paints, the agency said.
Regional work safety authorities were investigating the cause of the blasts.
Workplace accidents are common in China, with thousands of people killed every year.
Explosions and other industrial accidents are usually blamed on insufficient safety equipment and workers ignoring safety rules.