One person has been killed, two are missing and dozens are believed injured following an explosion Monday at a steel plant in Clairton, Pennsylvania, on the outskirts of Pittsburgh, officials said.

Allegheny County Emergency Services and the Allegheny County Police were responding to the blast at the U.S. Steel Clairton Coke Works plant, the groups said in a social media statement.

"At this point, officials can confirm there has been one fatality in connection with this incident. Two people are currently believed to be unaccounted for, and multiple individuals have been treated for additional injuries," the statement said.

First responders were trying to rescue people trapped in the rubble, the Associated Press reported, adding that the number of injured is in the dozens.

Construction worker Zachary Buday, who was near the steel plant, told WTAE-TV in Pittsburgh the explosion "sounded like thunder."

"It shook my chest. It shook the building, then we saw the dark smoke rising from the steel mill," he said. "Put two and two together. It's like something bad happened.''

The moment of the explosion, followed by large plumes of smoke shooting high into the air, is captured live in video from the BreatheProject, a Pittsburgh-based nonprofit that advocates for improvements to air quality in southwestern Pennsylvania.

Gov. Shapiro says 'multiple explosions' took place at plant

Pennsylvania Gov. Josh Shapiro said on social media the steel plant was the site of "multiple explosions,'' and that his administration will provide whatever resources are required.

"Injured employees have now been transported to local hospitals to receive care, and search-and-rescue efforts remain active at the plant,'' Shapiro said. "If you’re in the area, continue to follow the instructions of local authorities.''

U.S. Sen. John Fetterman of Pennsylvania said on social media he went to the plant Monday and gathered information from U.S. Steel and the steelworkers union.

"There is an active search and rescue underway, dozens injured, and per police there’s at least one unaccounted for,'' he said.

Residents near plant advised to stay indoors

The Allegheny County Department of Health issued a statement saying it was "actively monitoring the explosion" in coordination with first responders.

Residents within one mile of the plant were being advised "out of an abundance of caution" to remain indoors, close windows and doors and set their home cooling units to recirculation. Air quality monitors had not detected levels of toxins above federal standards, the department said.

Two workers at steel plant injured in February fire

A fire at the plant Feb. 5 injured two workers after a buildup of gases ignited, the Allegheny Front reported.

The Allegheny County Health Department said in a statement at the time that the incident was the result of a “hydraulic failure in a switch of the batters which led to a buildup of combustible material,” which then ignited.

The statement said a “boom” was heard and emissions leaked from the facility. The workers received first aid at the plant, were taken to a local hospital and released, the Allegheny Front reported.

The Allegheny County Department of Health has a webpage that includes recent legal actions dating to 2018 against the plant, including penalties for emissions violations, leaks and process and equipment failures.

Where is U.S. Steel Clairton Coke Works?

Clairton is about 20 miles south of Pittsburgh. The Clairton Plant is the largest coke manufacturing facility in the country and serves the commercial coke market as well as U.S. Steel's steelmaking facilities, according to U.S. Steel.

The plant operates 10 coke oven batteries and annually produces more than 4 million tons of coke, a type of fuel used in the steelmaking process, per U.S. Steel.

What is a coking plant?

A coking plant turns coal into coke, which is in turn used to make steel in a blast furnace. The coal is softened, then liquified and re-solidified into coke. Coal in a coking plant is heated without oxygen to temperatures as high as 1,125 degrees Fahrenheit, removing its impurities. The resulting coke is a porous, carbon-heavy material.

This article originally appeared on USA TODAY: Explosion 'like thunder' rocks Pa. steel plant; 1 dead, multiple injuries: Live updates

Reporting by Melina Khan, Jorge L. Ortiz and Phaedra Trethan, USA TODAY / USA TODAY

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