An explosion at a US Steel plant in Pennsylvania, near Pittsburgh, has killed two people and injured at least 10 on Monday, officials said.

The body of one worker was pulled from the wreckage hours after an explosion that sent black smoke spiraling into the sky in the Mon Valley, a region of the state synonymous with steel for more than a century. Allegheny county emergency services said a fire at the plant started around 10.51am. Authorities later said a second person had died.

Abigail Gardner, the director of communications for Allegheny county, told local news station TribLive that “a search-and-rescue operation” was under way after the blast.

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.

“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.”

Pennsylvania governor Josh Shapiro said in a statement on X: “My administration is in touch with local officials in Clairton … as they respond to an explosion at US Steel Clairton Coke Works plant [Monday] morning.”

He said Pennsylvania’s emergency management agency and its state police were in “touch with first responders and have offered all assistance”.

John Fetterman, a Democratic Pennsylvania US senator who formerly served as the mayor of nearby Braddock, called the explosion “absolutely tragic” and vowed to support steelworkers in the aftermath.

“I grieve for these families,” Fetterman said. “I stand with the steelworkers.”

Clairton’s mayor, Richard Lattanzi, said his heart went 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.”

The Clairton Coke Works, a huge industrial facility along the Monongahela River about 20 miles (32km) south of Pittsburgh, is considered the largest coking operation in North America.

The plant, which is part of US Steel and more than 120 years old, bakes coal at high temperatures into a pure carbon form that is then used in blast furnaces to turn iron ore into liquid iron used to make steel.

The Clairton plant supplies coke to US Steel’s mill in Gary, Indiana, and has previously been subject to concerns about safety and pollution.

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 2019, it agreed to settle a 2017 lawsuit for $8.5m. Under the settlement, the company agreed to spend $6.5m to reduce soot emissions and noxious odors from the plant.

In June, US Steel and Nippon Steel announced they had finalized a “historic partnership”. The deal came a year and a half after the Japanese company first proposed its nearly $15bn buyout of the US steelmaker.

The deal was approved with a caveat issued by Donald Trump in a June executive order, in which the president said he “reserved my authority to issue further orders with respect to the purchasers or US Steel as shall in my judgment be necessary to protect the national security of the United States”.

The Breathe Project, a south-western Pennsylvania group working to improve air quality in the region, warned the facility was likely emitting hazardous air pollutants, including asbestos, heavy metals and possibly benzene.

“This is the third major event at this plant in 2025. There was a stack explosion on February 2, 2025. A pollution control room malfunction on June 2-3, 2025 took pollution control equipment offline for an extended period of time. There were no known major documented injuries from these prior two incidents. Unfortunately, the incident today is more dire,” it said in a statement.

“Many people have been concerned about this facility and the community that hosts it for a long time. For decades, workers and residents across Western Pennsylvania have heard lofty promises from US Steel – many of which are later delayed or abandoned – and often delivered without transparency or meaningful community involvement,” it added, warning: “Problems have been ongoing with the facility, piling tragedy upon tragedy.”

Associated Press contributed reporting