UK police have been dispatched to "a major police incident" on London Bridge, where it appears a van traveling at a high speed may have deliberately crashed into pedestrians.
According to social media accounts, a white van plowed into pedestrians on or near the bridge, injuring several.
There are also unconfirmed reports of a stabbing attack.
BBC reporter Holly Jones was in the area when the attack occurred.
She told the BBC that a man was driving the van, which was "probably traveling at about 50 miles an hour" when it apparently began mowing down pedestrians.
Jones said the van struck five or six people, and that she witnessed a man later being taken away in handcuffs.
Other estimates say many more have been injured, and a witness told Reuters she saw people with what seemed to be knife wounds at the scene of the incident.
Armed police are at the scene of the apparent attack, along with helicopters and ambulances.
Witnesses describe the scene as "horrific."
The managing editor of The Spectator was apparently on the scene when the incident occurred and is reporting that he saw two casualties, one on the pavement and one in the road, according to British media.
London Bridge is closed in both directions and the London Bridge rail station has also been closed.