Heavily armed, masked police surrounded a site in central London on Friday after a woman reported that a mentally unstable man had walked into her office threatening to blow himself up.
Scotland Yard said in a statement that police were called to Tottenham Court Road, a busy central Londonavenue, just before noon and had sent a negotiator to the site. Office supplies, including computer monitors, were being thrown from the building's fifth floor window.
The area was cordoned off, nearby buildings were evacuated and a police sniper was stationed on a rooftop near the building.
"It's unclear if other people (are) in the building," police said in a statement.
Police said they aren't treating the incident as terror-related.
The Huffington Post, whose offices are just off Tottenham Court Road, said its building was among those evacuated. It quoted one witness as saying that a man had walked into her office "strapped up in gasoline cylinders."
"Basically he threatened to blow up the office," Abby Baafi, 27, told the website. "He said he doesn't care about his life, he doesn't care about anything, he's going to blow up everybody."
Baafi, whom The Huffington Post identified as an employee of the training company Advantage, said she recognized the man as a former customer.
"He's not quite stable, not mentally stable," she said.