TOTTENHAM Court Road has been evacuated after a man sparked an armed siege in central London.
Police have sent a negotiator after reports of a man throwing furniture out of a window several floors up of the block that houses the online news site Huffington Post.
Some people near the scene have reported the sound of shots being fired.
Huffington Post UK executive editor Stephen Hull posted a video on Twitter of an office worker who saw the man enter the building.
Abby Baafi, 27, the head of training and operations at Advantage, a company which offers HGV courses, told Mr Hull the man had targeted her offices and was currently holding four men hostage.
In a video posted on YouTube, she said: "What happened is, we were in the office and someone came in. He asked him what his name was and he said it was Michael Green.
"I recognised him because he was one of our previous customers but he is not quite stable - mentally stable.
"He turned up, strapped up with gasoline cylinders, and threatened to blow up the office.
"He said he doesn't care about his life. He doesn't care about anything, he is going to blow up everybody.
"He was specifically looking for me but I said 'My name's not Abby' and he let me go."
Ms Baafi said the man failed the HGV training course and wanted his money back.
Joaqam Ramus, who works at nearby Cafe Fresco, said before being evacuated: "There was talk of a bomb and somebody having a hostage in a building.
"All Tottenham Court Road is closed and so are we - the police told us to shut.
"We don't know what it is but it seems someone has a hostage."