A man has been shot by police near London Bridge in an incident which is being responded to “as though it is terror-related”, the Metropolitan Police said.
Footage on social media appeared to show armed officers surround a person on the ground before discharging a weapon, while a bystander appears to remove a large knife from the scene.
The eyewitness video appears to show a man being shot on the pavement of the north-bound carriageway on the western side, near Fishmongers’ Hall.
A Scotland Yard statement said: “At this stage, the circumstances relating to the incident at London Bridge remain unclear.
“However, as a precaution, we are currently responding to this incident as though it is terror-related.
“One man has been shot by police.”
Police believe a number of people have been injured.
No further details about casualties were available, although the London Ambulance Service declared it a major incident.
Witnesses described a scene of panic around London Bridge, moments after the incident.
Witness Kelby McNally, OK! Online’s editor, works in the Northern and Shell Building on Lower Thames Street near to London Bridge, said she initially thought a fire alarm had gone when she saw “loads of people just running”.
She told the PA news agency. “There were loads of people just running, I thought it was a fire alarm or something, and then I saw two girls from my office who told me not to go back there.
“I asked what had happened, and they said they had heard gunshots and now everyone is running.”
Prime Minister Boris Johnson said: “I’m being kept updated on the incident at London Bridge and want to thank the police and all emergency services for their immediate response.”
Home Secretary Priti Patel wrote on Twitter: “Very concerned by ongoing incident at London Bridge. My thoughts are with all affected. I am grateful for the rapid response of our police and I urge everyone to follow their advice.”
Footage from the scene appeared to show a white lorry straddling the northbound and southbound carriageways.
The video shows several officers surrounding the vehicle before moving to the rear to check its container.
London buses can be seen either side of the lorry while three police cars are parked next to it on the bridge.
Nurse Jackie Benfield, 32, described how she asked to be let off a bus on London Bridge after she heard “five or six” gunshots.
Ms Benfield, who was on her way home from work, said she exited the bus and “ran like hell” to escape the shots.
Connor Allen, who was in his van on the bridge when it was evacuated said: “Everyone just started running, you heard these pops and that was it. We just got out the van and started running.”
One business owner told the PA news agency she had been crossing London Bridge to get to her shop on the north side when police officers stopped her.
She said that was when she heard at least five or six gunshots and said that her store has been evacuated.
The woman, who wished to remain anonymous, said: “We heard shooting, it was about five or six shots, I heard five or six quite clearly.
“All my staff have been evacuated.”