LONDON (Reuters) - Historic theatres in London's West End were undergoing checks on Friday after the ceiling of one collapsed, injuring dozens and raising fears about safety at some of the world's oldest and most elegant playhouses.

Up to 90 people were injured, seven seriously, after a section of ornate plaster ceiling measuring about 10 meters (33 feet) by 10 meters fell onto the audience at the 112-year-old Apollo Theatre during an evening performance on Thursday.

Some of the 720-strong audience watching the popular play The Curious Incident of the Dog in the Night-Time told Reuters of panic and screams as the ceiling collapsed, filling the theatre with dust as they rushed for the exits.

It was the worst accident in London's main theatre district in 40 years, since part of a ceiling at the Shaftesbury Theatre fell in 1973, forcing the closure of the long-running musical Hair. The Shaftesbury opened in 1911.

Mayor of London Boris Johnson said investigations into the cause of the ceiling collapse at the Apollo were continuing. Westminster City Council and the Society of London Theatre (SOLT) had assured him that safety checks were up-to-date at all the West End's 30 or so theatres.

"But, as a precaution, further checks have already started and will continue throughout the day," Johnson said.

Some of the theatres date back to the 19th century and feature plush red velvet seating, ornate plaster ceilings, massive chandeliers and royal boxes.

A spokesman for SOLT said all major theatre owners met on Friday and confirmed their safety inspections and certificates were current, adding that such incidents were extremely rare.

"(They) will co-operate fully with the authorities to reassure the public that their theatres are safe," the spokesman said in a statement.

While the Apollo - situated in Shaftesbury Avenue, in the heart of the West End - will be closed this weekend, all other London theatres remain open for business.

London's West End is one of the world's largest and most prestigious theatre districts, rivaling New York's Broadway and entertaining over 32,000 people in central London every night, including many tourists. Annual attendances total 14 million.

SOLT estimates the 52 major theatres across London and countless smaller venues account for about 41,000 jobs in the capital, bringing in 2 billion pounds ($3.2 billion) a year.

But with many auditoriums aging, the industry has called repeatedly over the past decade for public investment to bring them up-to-date. A 2003 report by the Theatres Trust called for 250 million pounds to be ploughed into the venues.

"It got quite close to the government funding them and then the (2012 London) Olympics happened and the money went away," Alistair Smith, deputy editor of industry newspaper The Stage, told Reuters.

"The theatre industry has been aware of the need for some kind of public funding for theatres, not necessarily for safety reasons but to ensure these historic buildings are still around for another century or so."