LONDON — British officials were trying to establish Friday what led to the collapse of the ceiling at the packed Apollo Theatre in the heart of London's West End, injuring at least 76 people.
Investigators are still assessing the damage and trying to find out what happened.
An initial report is expected Friday. There are some reports, not confirmed, suggesting that water, possibly as a result of a passing thunderstorm, was seen dripping through cracks in the ceiling before it fell down.
More theaters are now being examined to make sure they are safe.
"Our theaters entertain over 32,000 people in central London every night and all theaters take the safety of their audience, performers and staff very seriously," the Society of London Theatre, an organization that represents London theater producers, owners and managers, said in a statement Friday.
The society said that every theater "undergoes rigorous safety checks and inspections by independent experts, and incidents like last night are extremely rare."
An initial structural assessment concluded that the building that houses the Apollo Theatre is secure.
Nimax Theatres, which owns the Apollo as well as a number of other theater venues across London, has described the incident as "shocking and upsetting."
There were no life-threatening injuries although seven people were said to have suffered serious injuries.
Eyewitnesses described chaos and panic as large hunks of plaster and dust rained down on the audience 45 minutes into a performance of "The Curious Incident Of The Dog In The Night-Time."
On Friday, the BBC tweeted a picture of what may be the first image from inside the theater after parts of the ceiling fell down on members of the audience.