Allegheny County Emergency Services said a fire at the plant in Clairton started late Monday morning. Officials said they had not isolated the cause of the blast.

One person has died, one person is unaccounted for and at least 10 are injured following an explosion at a U.S. Steel plant near Pittsburgh, Allegheny County Police Assistant Superintendent Victor Joseph said at a press conference Monday afternoon.

“It is with profound sadness that I share with you that the U. S. Steel colleague who had been unaccounted for has been located and confirmed deceased, following an extensive search and rescue effort," David Burritt, the company's CEO, said in a statement. At least 10 people were injured in the blast, officials said.