"We have arrested a man at Tottenham Court Road. A search of the building is under way," the Metropolitan Police said.
Witnesses had reported the man had taken four men hostage, but police said they were "not aware of any hostages at this stage."
Police had placed a 300-metre cordon around the building after the man, reportedly with gas canisters strapped to his body, entered and started throwing computer monitors from a window on the fifth floor.
Hundreds of local office workers watched throughout the three-hour siege from behind the cordon as monitors and papers were hurled intermittently from the window.
A police negotiator was sent to the building while armed officers patrolled the scene.
The incident, which started at 1100 GMT, was not terrorism-related, police said.
The Huffington Post website, whose offices are nearby, reported that the man had stormed into the offices of a company that offers courses on driving trucks.
The website carried a video interview with an employee of the company, Abby Baafi, 27, who said the man had targeted her company's offices.
"He just turned up, strapped up in ... gasoline cylinders. Basically he threatened to blow up the offices. Says he doesn't care about his life, doesn't care about anything," she said in the video.
COMMENTS
Comments are moderated and generally will be posted if they are on-topic and not abusive.
For more information, please see our Comments FAQ