Pictures said to show a fireball in Dongying, in the eastern province of Shandong, circulated on social media. Their authenticity could not be immediately verified.
The explosion occurred on Monday night at the Diao Kou Xiang Bin Yuan Chemical Co., according to a news website run by the local government.
The fire was extinguished about five hours later and "people in charge of the company" were detained by police, the site said.
The disaster sparked widespread outrage over alleged safety violations and possible official collusion, and fears of pollutants contaminating the air and water of Tianjin, home to about 15 million people.
Another explosion at another chemical plant in Shandong killed one person and injured nine on August 23.