Rescuers were continuing to search for one missing worker at the Clairton Coke Works more than five hours after mid-morning explosions rocked the Mon Valley plant. The blasts killed one person and injured 10.

One person has died and dozens are reportedly injured or trapped under rubble following an explosion at a U.S. Steel plant near Pittsburgh on Monday, an Allegheny County emergency services spokesperson told the Associated Press.

Authorities said 10 other workers required hospital treatment — including five listed in critical but stable condition — after an explosion Monday morning at the U.S. Steel Clairton Coke Works. The cause of the blast has not been determined.