Suicide at Blaine bridge

The crowds gasped as the man leaped from Tower Bridge, close to where the American is nearing the end of a 44- day stint without food in a glass box suspended over the river.

Fans using mobile phones alerted police and lifeboat crews who launched a major search of the river, supported by a police helicopter.

Hundreds of people were at the site of the stunt in Central London when the tragedy happened.

An eyewitness said: 'One minute we were watching David Blaine, the next minute my attention was caught by a man standing a quarter of the way along Tower Bridge, on the parapet. He appeared to drink something and then leapt into the water.

' There was a gasp from the crowd around the Blaine set as they realised what was going on.'

A Scotland Yard spokesman confirmed that fans of the magician had alerted emergency services.

He said: 'At 4.40pm we were called to the David Blaine site after reports of a man seen falling into the Thames.

'The Thames Division of the River Police and the RNLI are currently participating in a sweep of the river.

'The man appeared to be in his 20s. They will continue searching until they find him.'

Experts were studying tidal charts in a bid to establish where the man's body may be washed up. Police are also trying to establish his identity.

The tragedy is the latest in a string of incidents around David Blaine's endurance display.

The 30-year-old New Yorker has been the target of extensive ridicule from the public, with eggs and golf balls hurled at his glass box and many people holding up food for him to see.

One man was prosecuted for damaging a unit supplying his water.

The Metropolitan Police has said Blaine will be asked to pay the cost of policing his stunt.