Several people were injured in a roof collapse during a show at the Piccadilly Theatre in London’s West End.
The venue in Denman Street was packed for a performance of the Arthur Miller play Death of a Salesman.
Screaming was heard from the circle when the partial ceiling collapse happened just before 20:00 GMT. Some theatre-goers left covered in debris.
More than 1,000 people were evacuated from the venue, the Met Police said.
Five members of the audience needed hospital treatment for minor injuries, Ambassador Theatre Group (ATG) said.
Wendell Pierce, who plays Willy Loman in the show – which only opened on Monday – apologised to those who had been evacuated.
A video shared on social media shows the US actor outside the theatre asking the crowd to come back and see the play another time.
“We’re so honoured that you came tonight. We are so sorry that this happened,” he said.
BBC journalist Iain Haddow, who was in the audience, said the collapse happened about 20 minutes into the show.
He said that before the collapse there had been a steady drop of water “which turned progressively into a stream” – although it was not raining at the time – and said there was some panic when the ceiling fell in.
Outside the theatre, including on the roof, he said there was scaffolding and building work going on.
Following the collapse, an ATG spokeswoman confirmed the section of ceiling collapsed in the rear upper circle, at 20:00 GMT.
“The performance was immediately stopped and the theatre safely evacuated,” she said.
“We take the safety and security of our audiences extremely seriously and we are doing everything we can to ascertain the cause of the incident.
The theatre group has not yet made any announcement on when the venue will reopen and whether any shows or ticket-holders will be affected – but indicated a statement would be made later in the day.
In December 2013, 76 people were injured, seven seriously, when part of a ceiling at London’s Apollo Theatre collapsed during a show.
London Fire Brigade said three fire engines and three rescue units were at the scene on Denman Street and investigations were taking place.
Police added that road closures have been put in place and advised motorists to use alternative routes.