A fire broke out Monday in the Broadway theater that hosts the The Book of Mormon, forcing the long-running musical to close, at least temporarily, as the historic venue undergoes repairs.

The blaze, which began in an electrical room, caused “substantial damage” to the Eugene O’Neill Theatre, according to David Simms, New York fire department assistant chief. The cause of the fire remains under investigation.

“This was a deep-seated fire, involving a lot of electrical equipment,” Simms added. “It was very difficult to get to. There was a lot of catwalks and rigging in the theater.”

“Everyone has been safely removed from the theater,” the building’s owner, ATG Entertainment, said in a statement. “We will keep all parties abreast of this developing situation.”

The statement added that those involved with the production would “take time to assess the extent of the damage, and any news of disruption to performances will be announced as soon as possible”.

It was not immediately clear how long the 1,108-seat theater would be out of operation. A spokesperson for the The Book of Mormon did not immediately respond to messages. The show’s next scheduled performance is Tuesday.

Simms said the damage was largely confined to the fourth-floor area and a backroom containing lighting equipment and dangling chandeliers. There was some water damage as well, he said.

Firefighters initially struggled to suppress the flames due to catwalks and rigging in the theater, but were eventually able to bring it under control, the spokesperson said. One firefighter suffered minor injuries.

The Book of Mormon is among Broadway’s longest-running shows, with more than 5,000 performances since opening at the Eugene O’Neill Theatre in 2011.

The theater, which opened in 1925, has previously hosted productions of Sweeney Todd, a revival of Tennessee Williams’s Cat on a Hot Tin Roof and the rock musical Spring Awakening, among many other performances.