London (CNN) -- Police have arrested the man believed to be at the center of a security alert Friday that closed a major shopping street in central London, a police spokesman said.
After the arrest, officers searched the building on Tottenham Court Road to make sure it was safe, the Metropolitan Police said.
No hostages have been identified, police said.
"After contact with our specialist police negotiators the man came out of the building, and was arrested," Commander Mak Chishty said in a written statement. "He is now in police custody.
"Items were thrown from the window onto the street below," Chishty added. "We were concerned that he may have explosive materials or flammable liquids with him. Our immediate concern was for the safety of the people inside the building and for the general public in the vicinity.
"During the course of the incident a number of people who were inside the building left peacefully," he said.
Earlier unconfirmed eyewitness reports suggested the man might have had some kind of canister attached to his body and had threatened to explode it.
A Metropolitan Police spokesman earlier told CNN the police did not know if the man, age 49, was armed.
Officers carrying some kind of weapons -- it is not clear whether they were live firearms or stun guns -- were sent to the scene. Police do not commonly carry firearms in Britain.
A vehicle labeled "police explosive search dogs" also arrived and dogs could be seen on the closed-off street.
A 300-meter (980-foot) cordon was put in place on Tottenham Court Road, London's Metropolitan Police said.
The police declined to confirm reports that a sniper was positioned on a nearby roof.
The alarm was first raised around noon, with reports of a man causing a disturbance and throwing objects from an upper floor window. Police said electrical equipment was among the items tossed to the street below.
Unconfirmed eyewitness reports suggest the man entered an office building housing an employment agency.
The man, who appeared to be unstable, had some kind of canister strapped to him and threatened to blow it up, the witnesses said.
A police spokesman confirmed the force had received reports from the public suggesting the man had canisters attached to him but said officers could not confirm that themselves.
A tweet from the Metropolitan Police said: "There are no reported injuries and it's unclear if other people in the building."
A number of buildings in the area have been evacuated and half a dozen ambulances are at the scene. They have not yet been put to use.
The incident caused major disruption on a street usually busy with traffic, shoppers and local workers on their lunch break.
"We advise people to keep clear of the area due to congestion," the police said via Twitter.
Warren Street Underground station has been closed at the request of the police, Transport for London said. Goodge Street Underground station, which was closed because of the alert, was reopened shortly after the arrest.
Buildings used by students at University College London and a big London hospital are in the area.
The alert comes three months ahead of the Olympic Games in London, when a major security operation will be in place.
CNN's Raja Razek, Nic Robertson and Claudia Rebaza contributed to this report.