Workers were pushing coke out of huge ovens and preparing for maintenance when an explosion rocked a US Steel plant outside Pittsburgh, a company executive said Tuesday, a day after the blast killed two workers.

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.