At least 76 people were injured, seven of them seriously, when the ceiling of a 112-year-old theatre in the heart of London collapsed last night, leaving children and adults bleeding in the rubble amid scenes of chaos and panic.

Apollo Theatre, one of the popular venues in West End theatre district, was packed with about 720 people for a show of “The Curious Incident of the Dog in the Night-Time”, when plaster and masonry from a section of the ceiling fell with a crackling sound and left many wounded, including some with head injuries.

Paramedics initially said 88 people were injured but later revised the number to 76, seven of whom were seriously wounded. Another 51 “walking wounded” were taken to hospital with minor injuries.

London Ambulance on Friday said all those who had been trapped inside were freed. It was later confirmed that none of them had life-threatening injuries. Some 25 ambulance crews and an air ambulance attended the scene.

Some reports suggested that water began dripping through cracks in the ceiling before it came down.

There had been suggestions that the collapse may have been caused by a freak lightning strike, but London Fire Brigade said it had no records on its internal log of lightning.

London was hit by a freak thunderstorm last evening, which seems to have resulted in the incident at the building but the exact cause of the collapse is yet to be confirmed.

“There is no suggestion at this stage that this was as a result of a criminal act, however, at this stage we of course are keeping an open mind. Police are in liaison with Westminster City Council and structural engineers to establish how safe the building is before a full assessment can be carried out,” the Metropolitan Police said in a statement.

Deputy Assistant Commissioner Graham Ellis of the London Fire Brigade said the plasterwork had fallen onto the upper circle, the dress circle and the stalls.

“The injuries to the casualties that our colleagues have spoken about are consistent with that. We’ve managed to stabilise the situation inside the theatre. We’re working closely with colleagues at Westminster City Council, their building surveyors,” he said.

The theatre has since been declared secure after a structural assessment was carried out last night.

A district surveyor from the local council examined the damaged roof of the Grade II listed building and confirmed it was not at risk of caving in further.

Investigations are still underway into what caused a large section of ornate plasterwork to collapse.

A spokesperson for Nimax Theatres, which owns the Apollo, said their “thoughts are with the audience and staff”. The theatre’s owner described the incident as “shocking and upsetting”.

 

“Firefighters worked really hard in very difficult conditions and I’d like to pay tribute to them. They rescued people from the theatre, made the area safe and then helped ambulance crews with the injured. In my time as a fire officer Ive never seen an incident like this,” Kingsland Fire Brigade station manager Nick Harding said.

“I imagine lots of people were out enjoying the show in the run-up to Christmas. My thoughts go out to all those affected,” he said.

The historic theatre,named after the Greek and Roman god of the arts,opened in 1901.

It seats 755 on four levels and the balcony on the third tier is considered the steepest in London. Martin Bostock, who was in the theatre, told “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.”

Another Indian-origin theatregoer Khalil Anjarwalla told the BBC that his heavily pregnant wife and her parents managed to escape from the theatre safely after “kilos of concrete plummeted from the ceiling”. British Prime Minister David Cameron tweeted:”I’ve been updated regularly on the Apollo incident. I’m grateful for the fast work of the emergency services in helping the injured.”

The play, based on the novel of the same name by Mark Haddon, has been running to packed audiences in London since August 2012.

The show started at The National Theatre, before transferring to the Apollo in March this year.

Haddon tweeted: “It’s been horrifying sitting here watching what has been happening at the Apollo…I’m hugely relieved that no-one has died.” London Fire Brigade said it sent eight fire engines and three fire and rescue units to the scene with a total of about 60 firefighters.

Scotland Yard said many of the wounded were treated at the nearby Gielgud Theatre, while three London buses were used to transport others to hospitals.

The collapse took place despite a UK law which requires historic theatres such as the Apollo to have their roofs safety checked every three years.

It has raised concerns for the safety of other historic theatre buildings. Westminster City Council said it would be working with other theatres throughout the day to ensure all possible safety measures were in place.