LONDON, Dec 19 -- Some 88 people were injured, including 7 serious cases, after part of the roof in London's Apollo Theatre collapsed on Thursday.

London Ambulance said it treated 88 for injuries, 81 of whom had suffered minor wounds and seven with more serious injuries were taken to hospital. All trapped people had been freed, and there were no reports of fatalities, according to BBC.

A spokesman said the theater was almost full with 720 people watching the performance. Fire crews and ambulances were at the scene as a rescue opearation was under way.

British Prime Minister David Cameron said in a twitter message that he had been updated regularly on the incident, and "grateful for the fast work of the emergency services in helping the injured."

A spokesman for London Mayor Boris Johnson said: "He has spoken to the Met Police Commissioner and is liaising with the relevant agencies. His thoughts and prayers are with those involved in what is clearly a very serious incident."

The theater, which has 775 seats over four levels, first opened its doors in February 1901.