NEW YORK (AP) — A fire broke out Monday in the Broadway theater that hosts “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 New York Fire Department Assistant Chief David Simms. The cause of the fire remains under investigation.

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

It wasn’t immediately clear how long the 1,108-seat theater would be out of operation. A spokesperson for “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 knock down the flames due to catwalks and rigging in the theater, but were eventually able to bring it under control, he 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’ “Cat on a Hot Tin Roof,” and the rock musical “Spring Awakening,” among many other performances.