London's historic Apollo Theatre has been evacuated after part of the building's roof appeared to collapse, causing multiple injuries. Members of the public were attending a West End performance of The Curious Incident of the Dog in the Night-Time on Thursday (19Dec13), when debris began falling from the ceiling during the first half of the show. Emergency services were called to the Shaftesbury Avenue venue shortly after 8.15pm local time as people rushed towards the exits. A number of people were trapped by the falling concrete, but they have since been freed. A spokesperson for the London Fire Brigade has been sharing updates about the rescue mission via Twitter.com, writing, "It's thought there were around 700 people in the theatre on Shaftesbury Avenue in Soho. It's thought between 20-40 people were injured." Minutes later, the representative added, "all casualties who were trapped have been freed". Meanwhile, audience member Martin Bostock, who suffered a head injury in the incident, has described the panic and chaos that erupted as the drama unfolded. Speaking to Britain's Sky News, he said, "It was just terrifying and awful. I think the front part of the balcony fell down. At first we thought it was part of the show. Then I got hit on the head. "It was complete chaos in the theatre. Absolutely terrifying and awful. We got out with cuts and bruises. I think most people did." The Curious Incident of the Dog in the Night-Time play, adapted from author Mark Haddon's book of the same name, opened in the West End in March (13) under the direction of Marianne Elliott. The Apollo Theatre opened in 1901.