A rescue operation was under way Thursday night after part of a balcony or roof at London's Apollo theater collapsed in the middle of a show.

Several people were trapped by the debris, but all were freed as of 9:35 p.m. London time, said the London Fire Brigade.

Eyewitnesses said some people were leaving the theater bleeding. There were about 90 casualties, including walking wounded. Seven of them were seriously injured and required hospitalization.

Martin Bostock, who was in the theater, told the British network, "I was in the stalls with my family in the early stages of the show. I think the front part of the balcony fell down. At first we thought it was part of the show, it was very dramatic.”

"We got out with cuts and bruises, I think most people did," he added.

Simon Usborne, also watching the performance, told Sky News. "A huge crack happened ... and then my whole view of the stage was obscured by a huge cloud of dust.”

Usborne said people are being treated for head injuries.

"There are a lot of people with blood on their faces," he added.

The theater is located next to Picadilly Circus in the heart of the city in the Soho district, which is usually packed with tourists, shoppers and diners at theater time.