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.

The explosion ignited a fire and prompted a heavy response, including 15 county ambulances supplemented by police and fire units from surrounding towns. Video from local news outlets showed dense, black smoke rising above the Monongahela River.

Multiple people have been injured after an explosion Monday morning at the U.S. Steel Clairton Coke Works, and a rescue operation is underway to rescue trapped workers.