The Curious Incident Of The Dog in the Night-Time was being performed at the time, (8.15pm) when it happened. Eyewitnesses said they heard a crackling noise and then the ceiling collapsed.
An investigation is underway to find out the cause.
58 people had to go to hospital but luckily no one had any life threatening injuries.
The BBC reported that Incident commander Maria Smith, with the ambulance, who was one of the first on scene, said: "When I arrived it was dark and extremely dusty and people were lying on the floor of the theatre."
Nick Harding from London Fire Brigade said: "A section of the theatre's ceiling collapsed onto the audience who were watching the show. The ceiling took parts of the balconies down with it."
Image: Chris Edwards/BBC