An explosion occurred Monday at a steel factory in Clairton, Pennsylvania, authorities said. A spokesperson for Allegheny County said a rescue operation was underway at U.S. Steel Clairton Coke Works for people trapped under the rubble.

The plant, a massive industrial facility along the Monongahela River south of Pittsburgh, is considered the largest coking operation in North America and is one of four major US Steel plants in Pennsylvania.

The explosion, followed by several smaller blasts, could be felt in the nearby community and prompted county officials to warn residents to stay away from the scene so emergency workers could respond.