An explosion at a U.S. Steel plant near Pittsburgh left dozens injured or trapped under the rubble Monday, with emergency workers on site trying to rescue them, officials said.

There are no confirmed fatalities at the Clairton Coke Works, said Abigail Gardner, director of communications for Allegheny County. The explosion sent black smoke spiralling into the midday sky in the Monongahela Valley, a region synonymous with the state for more than a century.

“It felt like thunder,” Zachary Buday, a construction worker near the scene, told WTAE-TV. “Shook the scaffold, shook my chest, and shook the building, and then when we saw the dark smoke coming up from the steel mill and put two and two together, and it’s like something bad happened.”

Allegheny County Emergency Services said a fire at

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