A RESCUE operation is underway tonight after part of a balcony in the Apollo theatre in London's West End is thought to have collapsed during a performance, trapping people inside, according to eyewitnesses.

Police were called to the theatre in Shaftesbury Avenue shortly after 8.15pm.

A spokesman said: ''There is a report of a collapse in the building itself.''

It is thought around 30 people have been injured in the collapse, which occurred during a performance of The Curious Incident Of The Dog In The Night-time.

Eyewitnesses said they saw people being escorted out of the building, covered in dust and debris.

A Metropolitan Police spokesman said there were ''multiple casualties''.

London Fire Brigade confirmed that eight fire engines had been sent to the scene.

Martin Bostock, who was in the audience at the Grade II listed theatre with his family, said he suffered a head injury after he was hit by falling debris.

He told Sky News: ''I was in the lower stalls with my family in the early stages of the show.

'It was just terrifying and awful.

''I think the front part of the balcony fell down.

''At first we thought it was part of the show.

''Then I got hit on the head.''

He added: "It was complete chaos in the theatre. Absolutely terrifying and awful."

Walking wounded were taken from the scene in ambulances as a team of firefighters rushed through the front stage door in Archer Street.

Some were taken to the nearby White Horse pub, while others were taken from the scene to be reunited with friends and family members.

The Apollo Theatre is a Grade II listed building.