The death toll from a blast at an explosives plant in eastern China earlier this week rose to 33 Thursday as 20 missing people were declared dead, state media reported.

Officials had said Tuesday that the explosion, which occurred the day before in the Shandong province city of Shangqiu, had killed 13 people and left 20 missing.

Xinhua news agency reported Thursday, citing local rescue officials, that the 20 missing had also died, their identities confirmed through DNA tests.

The blast occurred at a three-storey workshop owned by Poly Explosives (Jinan) Co., Xinhua said. A total of 19 people were injured and were in stable condition in local hospitals, the report said.

The cause of the blast was under investigation.