Tottenham Court Road in central London has been sealed off by Met Police after a man started throwing furniture items out of an office window in the busy street at around noon (0700EDT) on Friday.
It is not clear at this stage if the man is armed or if he has taken hostages but police marksmen are currently in position on surrounding rooftops. The man who has been named in the last hour as Michael Green, 50, is occupying the top floor of an HGV (Heavy Goods Vehicles) driver training centre. Some witnesses have told the gathering media that he was threatening "to blow himself up and had a bomb", reports the BBC.
It is believed there are a number of canisters strapped around his body and it has been suggested that Green has some grievance with the training centre. Unconfirmed reports suggest Green is armed with flame-throwers and gas canisters.
Michael Green is believed to be holding four hostages at this moment - a company director and three salesmen at the training centre's headquarters. The offices are home to a logistics company called Advantage and Green had initially held five hostages but a pregnant woman pleaded for her life and was subsequently released.
Police have asked anyone who knows Michael Green to contact Holborn Police station.