An eyewitness who is on the 33rd floor of an office block a few hundred yards from the bomb scare seige in Tottenham Court Road says that another four ambulances, on top of the five to six existing ambulances have started arriving at the scene. Warren Street tube station in the busy shopping district in Central London has also been shut in the last few minutes.

Cassandra Williams, a business and legal affairs executive at media distribution company DCD Rights in the heart of central London, said: "We saw papers flying out the window and since then all the roads have been cordoned off, people have been evacuated from neighbouring buildings. Other than police, five to six ambulances and police vans, the place is deserted."

Williams said that all workers at her firm and the rest of her office block at the top of Tottenham Court Road, one of London's busiest streets, had been advised to stay in the building while the drama unfolds.

Armed police cordoned off Tottenham Court Road after reports that a disgruntled lorry driver had entered the offices of HGV licensing company Advantage and demanded his money back after he failed an HGV training course. He hurled objects out of the fifth-floor window on to the street below and, according to eyewitness accounts on social networking site Twitter, the man has thrown computers out the window.

A Metropolitan Police spokesman would not confirm that the man has a bomb.

A video of someone who was in the building when the man entered has been uploaded to Youtube.

"What's happened is we were in the office, someone came in and we asked him what his name was. I recognised him because he was one of our previous customers," said Abby Baafi, 27, the head of training and operations at Advantage, in the video recorded by Stephen Hull, executive editor of the Huffington Post UK who is at the scene.

"He just turned up in gasoline cylinders. He threatened to blow up the offices. He said he doesn't care about his life, he doesn't care about anything, he's going to blow up everybody."

She said he was looking for her, but he let her go because she said she was pregnant.