When American tourist Scott Daniels first heard the screams in London's Apollo Theatre, he thought they were part of the show, an acclaimed production of The Curious Incident Of The Dog In The Night-Time.
But soon it became obvious that something disastrous was happening in the packed theatre.
"All of a sudden, plaster starts raining down, huge hunks of plaster," said the Texas resident. "The lights went out and everything filled with dust - everybody was coughing and choking."
More than 75 people were injured - seven seriously, authorities said - when the Apollo's ceiling partially collapsed on Thursday night.
Daniels said he made it out with "a couple scrapes", though he saw others with bad lacerations.
The collapse at the Apollo Theatre took place around 8.15pm during a performance at the height of the Christmas holiday season. When plaster and masonry from the section of ceiling tumbled down, they brought parts of the theatre's balconies down onto the audience too, police said.
More than 700 people were in the theatre at the time, according to the London Fire Brigade.
Officials said most of the injured were "walking wounded" with upper-body injuries, and that all were conscious and breathing.
Police and fire officials said it was too soon to say what had caused the partial collapse of the ceiling, but that a full investigation was being carried out.
Dee Stephenson said she was seated near the stage and heard the main actor shout "watch out!"
"Then you could feel the debris literally coming down on you and then I got hit on the back by a large piece," she said. "It was a complete dust curtain. You couldn't see."
Dust-covered people, many with bandaged heads, were treated by dozens of emergency workers in the street outside the Apollo and at a nearby theatre.
Injuries ranged from head wounds to cuts and scrapes to breathing problems.
Initially, London Ambulance Service said more than 80 people had been injured. But noting that the initial situation was confusing, it later adjusted that number to say it had treated 76 patients, 58 of whom were taken to hospitals.
Video: London theatre ceiling collapses during show
Of those, 51 suffered minor injuries and seven had "more serious injuries". There were no fatalities and none of the injuries were believed to be life-threatening, officials added.
The fire department said no one was trapped in the theatre, explaining that rescuers had helped evacuate some people who had been trapped "by the nature of their injuries" where they had stood when the ornate plastering came down.
Chief Superintendent Paul Rickett said that "so far, we know that a number of items of masonry have fallen down from the ceiling.
"There is no suggestion at this stage that this was as a result of a criminal act. However, at this stage we are keeping an open mind."
The Apollo Theatre, named after the Greek and Roman god of music and the arts, was built in 1901 and has 775 seats. The show, which is aimed at young people as well as adults, is about a boy with Asperger's who sets out to solve a crime.
Prime Minister David Cameron said via Twitter that he was being updated regularly on the crisis. He praised the city's emergency services - who were on the scene within three minutes - for their "fast work" in helping the injured.
Nimax Theatres, which owns the Apollo, described the incident as "shocking and upsetting" and said an investigation into what caused the ceiling collapse was under way.