LONDON (ABC NEWS) -- A theatergoer at London's Apollo Theatre said that people began screaming in the middle of a performance as the ceiling began collapsing onto viewers today.
"We just saw things falling in front of us, big things, falling," Alexey Moskvin told ABC News. "People were screaming. I'm pretty shaken."
"It was very scary. There was so much stuff coming from the ceiling," he said.
The cave-in happened around 8:15 p.m. in London, or 3:15 p.m. ET. Audience members had packed into the theater to see a performance of "The Curious Incident of the Dog in the Nighttime."
The theater is located in the heart of London's "Theatreland" district, in the West End. It has 775 seats on four different levels and is one of London's oldest theaters.
Police said five people were seriously injured, with more than 40 "walking wounded."
"It was just a half-an-hour into the performance -- it's a great performance and initially when people started screaming my first thought was that it was part of the performance -- how wrong I was," Moskvin told ABC.
"It looked very serious from where we sat," he said. "Outside, a couple of people being taken away -- a few scratches."
Witnesses told the BBC that "within an instant, the entire roof caved in" on theatergoers.
London was hit by a severe thunderstorm about an hour before the performance began, according to the Associated Press.
The Apollo Theatre features one of the steepest balconies in London, according to the AP.