Scotland Yard said its armed officers shot dead a man "acting suspiciously" in Westminster near Trafalgar Square in central London on Sunday night.
The Metropolitan Police said the incident, which is not being treated terrorism, involved the suspect producing two knives before a Taser and firearm were discharged by police.
"Police officers were on patrol at around 23:25 hrs on Sunday, March 8, when they noticed a man who they believed to be acting suspiciously. Officers challenged the man who produced two knives," the Met Police said.
"Armed officers responded. Taser and a police firearm were discharged during the incident. London Ambulance Service attended and the man was pronounced dead at the scene at Great Scotland Yard short time later," the statement said.
Images from the scene show police lights flashing in the side road to Great Scotland Yard, the headquarters of the Met Police, where the man was shot.
"No police officers or members of the public were injured during the incident. Enquiries into the circumstances remain ongoing. The incident is not being treated as terrorism," the Met Police said.
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The UK's Directorate of Professional Standards and the Independent Office for Police Conduct (IOPC) have been informed as in every police shooting case in Britain.
The IOPC said: "At this early stage it is believed a man has been fatally shot during the police response to reports of a man carrying knives and acting suspiciously. Our thoughts and sympathies are with all of those affected by this terrible incident.