The theater has been presenting “The Curious Incident of the Dog in the Night-Time,” which was adapted from a mystery novel and is one of London’s most popular plays.

The collapse also brought down lights and rigging, and a large part of the ceiling fell nearly four stories onto the people sitting in the lowest level. Witnesses described a tapping or cracking sound, which many thought was part of the play, and then saw movement from those in the first rows of the balconies, before a large piece of ceiling smashed down, cutting the main lights and producing big clouds of dust, screaming and panic.

Steve George, who manages a movie theater, took his wife to the play for her birthday. They had balcony seats five rows back from the edge, he said. “We saw people at the front of the row get up and move, like the way people get up and move when they’re bored and leave,” he said. “Then it was like a ripple going backwards, literally in a matter of seconds. We heard a massive crash and the ceiling came crashing straight down in front of the balcony into the stalls. Some people were screaming, but in the section where we were there was no shoving or pushing. We realized it was serious when the emergency lights came on and there was a lot of dust. Ushers were guiding people out. It was a speedy walkout.”

Image The Apollo Theater, on Shaftesbury Avenue, opened in London in 1901.

His wife, Hannah, said: “It went very quickly. For a second I thought it was part of the sound effects; it was surreal. I realized when I saw all the dust.”