BEIJING (REUTERS) - Nine people were missing and two injured in a blast at an east China factory on Wednesday (Oct 21), state media said, the latest in a string of warehouse and plant explosions.

The frequency of blasts in China, including massive explosions that killed more than 160 people in the northeastern city of Tianjin in August, have raised questions about safety standards failing to keep up with three decades of breakneck economic growth.

The blast occurred at Shandong Tianbao Chemical Industry Corporation in Shandong province's Pingyi county, Xinhua news agency said, adding that the company made civilian-use explosive materials.

"The cause of the blast is being further investigated,"Xinhua said.

Chemical facilities explosions are relatively common in China and blasts have killed people since the Tianjin disaster, which spurred nationwide shutdowns and safety checks.