Emergency services personnel use a hydraulic lift to investigate the cause of a ceiling collapse at a theatre in Central London.
London theatres sought on Friday to reassure visitors about the safety of their buildings after the ceiling collapsed onto the audience at a packed show, injuring 76 people.
A sell-out crowd of 720 people was in the Apollo Theatre on Thursday night when 10 square metres of ornate plaster and masonry fell from the ceiling, taking a section of the balcony with it and striking audience members below.
An investigation is now under way, with one line of inquiry likely to focus on a thunderstorm and heavy rain that fell shortly before the ceiling fell in shortly after 8:00 pm.
Witnesses said they heard creaking noises in the 112-year-old theatre but thought it was part of the performance of "The Curious Incident of the Dog in the Night-time".
Then debris and dust filled the air, sending coughing, terrified theatregoers - many of them families enjoying a pre-Christmas treat - fleeing for the exits.
Rescuers commandeered three red London double-decker buses to transport the wounded, many of them with head injuries.
Ambulance staff said they treated 76 patients, taking 58 to hospital, including a number of children. Seven people had serious but not life-threatening injuries.
A surveyor examined the theatre overnight and said the roof was secure, but the local authority is still investigating what happened.
"We will not know the cause of the incident until all investigations have been completed but checks are ongoing," said Councillor Nickie Aiken of Westminster Council.
"This appears to be an isolated incident, but we will continue to work with theatres throughout the day to ensure that all safety precautions are in place."
All historic theatres are required to have their roofs checked every three years, and industry figures stressed that visitors to other theatres need not be concerned.
The Apollo cancelled all performances until January 4 but other shows across the capital will continue as normal, the Society of London Theatres said.
Plays and musicals are big business in London, enjoyed by estimated two million foreign visitors last year, according to the Visit Britain tourism agency.
Christmas is a particularly busy time, and the producers will anxiously be watching for any sign that the Apollo incident might scare off visitors.
A Society spokesman said all the major theatre owners held an emergency meeting on Friday morning where they confirmed their safety certificates were all up to date.
They said they would "co-operate fully with the authorities to reassure the public that their theatres are safe", he said.
Nimax Theatres, which owns the Apollo, said the ceiling collapse was a "shocking and upsetting incident".
Theatres become impromptu hospitals
Witnesses recounted the terror when the ceiling fell from the Edwardian-era theatre, which has three tiers of balconies, the uppermost of which is said to be the steepest in London.
Audience member James Kearney, who was given a ticket to the show as a present, recounted seeing "people with blood on their heads" behind him.
His companion Dee Stephenson said there was so much dust afterwards they had to feel their way out.
"Everybody was in a trance-like state. A lot of people were in absolute shock. We were extremely fortunate," she said.
Pictures from inside the theatre showed wooden beams and masonry piled on top of rows of dust-covered red seats.
A fire service spokesman said on Friday that a 10-square-metre area of the theatre's main plaster ceiling fell down, landing on the balconies and some of the main stalls.
Desmond Thomas, 18, part of a school party watching the show, said they heard noises before the accident.
"Maybe 10 minutes into the performance we heard a tap-tap noise, we thought it was rain," he told AFP.
"There was a crack and then it suddenly seemed to get bigger and suddenly it collapsed. The next thing we knew the whole theatre filled with dust and smoke."
Prime Minister David Cameron said was "grateful for the fast work of the emergency services in helping the injured".
Some of those hurt were treated in triage centres set up in the lobbies of the nearby Gielgud and Queen's theatres.
"In the finest traditions of Theatreland, they very quickly rallied around," said fire brigade spokesman Graham Ellis.