Armed police shot a man on London Bridge after several people were stabbed on Friday, reviving memories of a terror attack two years ago that killed eight.
Scotland Yard said they were treating the situation as “terror-related” as a precautionary measure while the ambulance services declared a “major incident”.
One man was being detained.
Britain’s Home Secretary Priti Patel, the interior minister, said she was “very concerned” at events while Prime Minister Boris Johnson cut short a visit to his constituency in northwest London.
Footage filmed by eyewitnesses circulating on Twitter showed a scrum of people surrounding a man on the ground.
One man wearing a coat and tie, retreating from the scene, appeared to be holding a knife in his right hand.
Three armed officers then appeared on the scene and surrounded the scrum. One officer pulled a man away before two shots appeared to be fired
Johnson’s spokesman said the premier was on his way back to his Downing Street office, where he would receive further updates on the incident.
In a brief statement, Johnson thanked the police and all emergency services “for their immediate response”.
Police said they were called at 1:58 pm (1358 GMT) to a stabbing at premises near the bridge, which in June 2017 was hit by a terror attack which killed eight and injured 48.
“At this stage, the circumstances relating to the incident at London Bridge remain unclear,” the Metropolitan Police said.
“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 said they were called just before 2 pm to a stabbing at premises near London Bridge.
“A number of people have been stabbed we will provide further details of those injured when possible,” a spokesman said in a statement.
“A man has been shot by police at the location,” the spokesman added.
– Bridge closed off –
An eyewitness told reporters: “He was on the ground with a knife near him, and a bag near him and then they surrounded him and armed police shot him.”
A BBC reporter on the bridge at the time said he saw what appeared to be a fight between a group of men, heard two shots and saw a man “prone” on the ground.
People in the area were quickly ushered away from the scene.
The bridge was closed off, with buses and traffic on London Bridge at a standstill. A white truck appeared to have jacknifed on the bridge.
One eyewitness told the BBC she and other people in the area rushed into a restaurant and were told by staff to take cover.
“They went, ‘Get under the table, shots have been fired. Gunshots’,” said the woman.
The 2017 attack involved Islamist extremists in a van who ploughed into pedestrians on London Bridge before attacking people at random in nearby Borough Market.
The three attackers, who were wearing fake suicide vests, were shot dead by police.
Borough Market and nearby London Bridge station were both shut as a precaution, according to the emergency services.
The Metropolitan Police were due to issue a statement outside their Scotland Yard headquarters.
Britain downgraded its terrorism threat level from “severe” to “substantial” on November 4, its lowest rating in more than five years.
British officials consider a terrorist attack “likely” when the threat level is substantial, and “highly likely” when it is severe.