CLAIRTON, Pa. (AP/WHTM) – One person has died and two are believed to be missing in the explosion at a U.S. Steel plant, Allegheny County emergency services spokesperson Kasey Reigner said.

Multiple other people were treated for injuries, Reigner said, after the explosion at the Clairton Coke Works.

The Allegheny County Emergency Services said a fire at the plant started around 10:51 a.m. and that it has transported five people. The agency did not provide any more details on those people transported and would only say it was an “active scene.”

The Clairton Coke Works, a massive industrial facility along the Monongahela River south of Pittsburgh, is considered the largest coking operation in North America.

Pennsylvania Governor Josh Shapiro says the Pennsylvania State Police and Pennsylvania Emergency Management Agency are “in touch with first responders and have offered all assistance.”

“Please join Lori and me in praying for the Clairton community,” the governor posted on social media.

U.S. Senator John Fetterman says he’s monitoring the explosion and waiting for more information.

“Keeping those injured and all who are impacted in my thoughts right now,” Fetterman said.

Fetterman was seen at the incident site on Monday afternoon talking to officials and reporters.

Lt. Governor Austin Davis shared that he knows people who work at the plant, and that he and his wife “are praying for the workers and their families.”

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 U.S. Steel plants in Pennsylvania that employ several thousand workers.

In June, U.S. Steel and Nippon Steel announced they had finalized a “historic partnership,” a deal that gives the U.S. government a say in some matters and comes a year and a half after the Japanese company first proposed its nearly $15 billion buyout of the iconic American steelmaker.

The pursuit by Nippon Steel for the Pittsburgh-based company was buffeted by national security concerns and presidential politics in a premier battleground state, dragging out the transaction for more than a year after U.S. Steel shareholders approved it.

In February, a problem with a battery at the plant led to a “buildup of combustible material” that ignited, causing an audible “boom,” the Allegheny County Health Department said. Two workers who got material in their eyes received first aid treatment at a local hospital but were not seriously injured.

In recent years, the Clairton plant has been dogged by concerns about pollution. In 2019, it agreed to settle a 2017 lawsuit for $8.5 million. Under the settlement, the company agreed to spend $6.5 million to reduce soot emissions and noxious odors from the Clairton coke-making facility, on the Monongahela River about 20 miles (32 kilometers) south of Pittsburgh.

The company also faced other lawsuits over pollution from the Clairton facility, including ones accusing the company of violating clean air laws after a December 2018 fire damaged the Clairton facility’s sulfur pollution controls.

Clairton Mayor Richard Lattanzi said his heart goes out to the victims of the explosion.

“The mill is such a big part of Clairton,” he said. “It’s just a sad day for Clairton.”