A rescue operation is underway for people trapped under rubble following an explosion at a Pennsylvania steel plant, county officials said.

It’s not clear how many people are trapped from the blast at the US Steel Clairton Coke Works plant in Clairton, about 15 miles outside of Pittsburgh.

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.”

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