Police have declared a knife rampage in central London as a terror incident and confirmed that the suspect was shot dead by armed officers on London Bridge.
Several people were stabbed by the knifeman before he was grappled to the ground and disarmed by members of the public.
Footage on social media appeared to show one man being pulled away by armed officers before the suspect is shot at point-blank range.
Another bystander could be seen carrying a large knife from the scene.
-> Live updates as multiple people stabbed on London Bridge
Eye-witnesses said the suspect appeared to be wearing a suicide vest but Neil Basu, the head of UK counter-terrorism policing, said the vest was a fake.
He said police were called at around 2pm on Friday to a stabbing "at a premises near London Bridge".
Borough Market, at the opposite end of the bridge to where the suspect was shot, was cordoned off in the wake of the incident.
The bridge and the market were the scene of a terror attack in 2017 in which eight victims were killed along with the three terrorists.
After being shot, the suspect in Friday's attack raised his arms towards his head before lying still.
Mr Basu told reporters: "A male suspect was shot by specialist armed officers from City of London police and I can confirm that this suspect died at the scene."
Scotland Yard said a number of people were stabbed but did not give any details.
The London Ambulance Service declared it a major incident and one picture on social media appeared to show a body covered with a blanket.
After speaking to reporters, Mr Basu said he was going to Downing St to brief the Prime Minister.
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 Bensfield, 32, described how she asked to be let off a bus on London Bridge after she heard "five or six" gunshots.
Ms Bensfield, 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."