A “number of people” are believed to have been injured amid a stabbing incident near London Bridge, police say.
There were multiple reports of shots being fired, possibly by officers, in the wake of the incident, which has seen the bridge evacuated and shut both ways.
A man has been detained by police following the incident.
London Bridge station has also been evacuated, while a cordon has been set up at Borough Market.
Response from officers led scores of people to run down St Thomas’ street, though the exact cause of the incident is still unknown.
The London Ambulance Service confirmed it was also responding to the incident, saying there were “crews on scene.”
Various social media users have reported hearing gunshots from London Bridge.
One video shows what appears to be police pulling equipment out of a vehicle nearby.
Those in the video can be heard saying: “They’ve actually got guns out. They’ve got the guns out.”
BBC correspondent John McManus told BBC News that he had heard several gunshots on London Bridge.
“There appeared to be a fight going on on the other side of the bridge, with several men attacking one man,” he said.
“Police then quickly arrived, including armed police, and then a number of shots were fired at this man.”
The bridge has been cleared by police, “but there are more shots going on,” McManus added.