AT LEAST one person has died and dozens injured after a massive explosion ripped through a steel plant in Pennsylvania on Monday.

An urgent rescue operation is underway to save workers who were left trapped under the piles of rubble left by the fiery boom.

Fire crews raced to the scene to battle the flames after the explosion at US Clairton Coke Works right outside Pittsburgh.

Many people were injured in the incident, and Senator John Fetterman said at least one person has died, according to CBS affiliate KDKA.

Terrifying aerial images show the piles of singed wreckage left by the explosion.

First responders say that workers are still trapped under the mountains of heavy materials, and that fire crews are trying to pull them out.

Pennsylvania Governor Josh Shapiro wrote that he is in touch with local officials as they continue to work through the scene.

“The scene is still active, and folks nearby should follow the direction of local authorities,” he said on X.

“Please join Lori and me in praying for the Clairton community.”

Lieutenant Governor Austin Davis also said that the state would be sending “whatever resources and manpower are needed” for the rescue.

‘FELT LIKE THUNDER’

A local who was working near the explosion described the terrifying moment he felt the ground-shaking boom.

“Felt like thunder,” Zachary Buday told ABC affiliate WTAE.

“It shook my chest. It shook the building, then we saw the dark smoke rising from the steel mill.

“Put two and two together. It’s like something bad happened.”

Clairton Coke Works is the largest coking operation in North America, according to the Associated Press.

Coking is the process of heating coal past 1,000 degrees to refine it into a more high-carbon product called coke.

The sprawling facility employs thousands of workers and is one of four major operations in Pennsylvania.