UPDATE 4:35PM EST: 

A theater in central London partially collapsed Thursday night during a performance at the height of the Christmas season, with police saying there were “a number” of casualties.

It wasn’t immediately clear if the roof, ceiling or balcony collapsed at the Apollo Theatre during a performance of “The Curious Incident Of The Dog In The Nighttime.”

Police said officers were called at around 2015 GMT (3:15 p.m. EST) to reports of a ceiling collapse at the theater on Shaftsbury Avenue in central London. It said police “are aware of a number of casualties,” but had no further details.

Witnesses told British media that the theater in London’s famous West End was packed during the holiday season to see the show, which is based on the best-selling novel by Mark Haddon.

“We thought it was part of the show, until something hit me on the head very hard,” one man told the BBC, speaking from the foyer of the theater while he was being evaluated by emergency workers. “I thought we were all going to be in really, really serious trouble.”

“Within an instant, the entire roof caved in,” another witness told the BBC.

London’s fire department said eight engines are on the scene in the SoHo neighborhood, and the city’s ambulance service said it had sent “a number” of crews to the theater.

Martin Bostock was in the audience with his family, and said “complete chaos” erupted in the theater.

“At first we thought it was part of the show,” he told Sky News. “Then I got hit on the head.”

The Apollo Theatre, named for the Greek and Roman god Apollo, god of music and the arts, was built in 1901 and has 775 seats.

London was hit by a freak thunderstorm about 7 p.m. that dumped heavy rain on the city, but it wasn’t immediately clear if that was related to the collapse.

On its website, the theatre warned that its balcony was one of the steepest in London “so avoid if you have trouble with heights.”

(AP)

Update 4;18 PM EST: 700 people were in London’s Apollo theater at time of tonight’s roof collapse. Shaftesbury Avenue has been cordoned off.

A Met spokesman said: “London Fire Brigade and London Ambulance Service are on scene.

“We have had reports of multiple casualties but no further detail at present.”

Simon Usborne, a writer, said there was a “cloud” of dust obscuring the stage after parts of masonry appeared to fall away.

He said: “There was panic, there was screaming.”

He added that there did not appear to be any sign of damage from the outside of the theater.

Update 4:16 PM EST: “There are a lot of people with blood on their faces”: Eyewitness account of the balcony collapse at Apollo Theatre

Update 4:10 PM EST: People in the theater have described the panic as the collapse of the roof brought down clouds of dust. Some said it was hard to breathe as they rushed for the exit.

A 38-year-old said: “We were in the stalls. It’s a balcony that’s come off. Some of the structure’s come down.”  Martin Bostock, who was in the audience at the Grade II listed theatre with his family, said he suffered a head injury after he was hit by falling debris. He told Sky News: “I was in the lower stalls with my family in the early stages of the show.  He went on: “It was complete chaos in the theatre. Absolutely terrifying and awful. We got out with cuts and bruises. I think most people did.”

Update 4:07 PM EST: Officials have released that over 30 people are injured due to the collapse.

London police say there are “a number” of casualties following the apparent collapse of a theater’s roof.

Police said officers were called at around 2015 GMT (3:15 p.m. EST) to reports of a ceiling collapse at the Apollo Theatre on Shaftsbury Avenue in central London.

It said police “are aware of a number of casualties” but had no further details.

London’s fire department said eight engines are on the scene in the SoHo neighborhood.

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(AP)