An explosion has killed one person and injured 10 others at the US Steel Clairton plant outside Pittsburgh, Pennsylvania, on Monday, officials say.

A major search and rescue operation is continuing for another person who is unaccounted for and believed to be under rubble.

Officials said they still do not know the cause of the explosion, and have requested locals keep their windows closed with smoke in the area.

The plant is the largest coking operation in North America, and is located about 15 miles (24km) south of Pittsburgh.

Governor Josh Shapiro posted on social media that the state's emergency management services and police had been deployed to the plant.

US Senator John Fetterman wrote on X that he was also at the scene and witnessed "an active search and rescue underway."

The plant is a major producer of coke, a coal-based fuel used in the production of steel. About 1,300 employees work at the facility, according to US Steel.

David B Burritt, President and CEO of US Steel, said in a statement that the company was "working closely with relevant authorities to investigate the cause of the incident".

He later told reporters at the press conference that the plant was "stable" but "it is still an active investigation."

"It's just a sad day for Clairton," Mayor Richard Lattanzi told the BBC's US news partner, CBS.

Clairton Coke Works has been dogged by pollution concerns throughout its history and has had to pay millions of dollars in fines, penalties, and settlements in recent years.

The plant's owner, US Steel, was fined nearly $2m (£1.5m) last year by the Allegheny County Health Department (ACHD) for processing and equipment issues with its coking ovens.

The ACHD also fined US Steel $2.2m in 2023 for exceeding Pennsylvania's standards on hydrogen sulphide emissions from the Clairton plant, and ordered them to provide officials with a plan to comply with state standards.

In 2022, Pennsylvania health officials fined US Steel $4.7m after it found the plant was not using a pollution control device for its coke pushing.