One person has died, two are believed to be unaccounted for and dozens are hurt following an explosion at a Pennsylvania steel plant on Monday, Allegheny County police said.

       The blast at the U.S. Steel Clairton Coke Works plant in Clairton, about 15 miles outside of Pittsburgh, trapped people under rubble, prompting a rescue operation, according to Allegheny County officials.

       The exact number of victims was not clear but many of the injuries are non-life-threatening, Allegheny County Emergency Services spokesperson Kasey Reigner said.

       Allegheny County Director of Communications Abigail Gardner said the Health Department is on site monitoring air quality and Gov. Josh Shapiro said his administration is in touch with officials.

       "The scene is still active, and folks nearby should follow the direction of local authorities," the governor said on social media. "Please join Lori and me in praying for the Clairton community."

       The Bureau of Alcohol, Tobacco, Firearms and Explosives is also responding, according to a spokesman.

       This is a developing story. Please check back for updates.

       ABC News' Michael Pappano contributed to this report.