A man has been arrested by armed police near the houses of parliament on suspicion of acts of terrorism, and knives have been recovered from him.
No injuries have been reported and police said the incident was no longer ongoing. Mayor of London Sadiq Khan said he had been briefed by the Met commissioner Cressida Dick on the arrest.
Pictures from the scene showed forensic officers examining knives on the pavement near where the arrest took place.
An eyewitness told BuzzFeed News he saw knives spill out of a backpack when the arrest was made.
Police said a 27-year-old man was arrested on suspicion of possession of an offensive weapon, and on suspicion of the commission, preparation, and instigation of acts of terrorism.
The Metropolitan police said he was arrested at 2:22pm following a stop and search as part of an ongoing investigation.
"He is being detained under the Terrorism Act and is in custody in a south London police station," the statement said.
"Detectives from the Counter Terrorism Command are continuing their investigation, and as a result of this arrest there is no immediate known threat."
The police statement in full:
A man has been arrested in Whitehall this afternoon, at approximately 14:22, following a stop and search as part of an ongoing operation.
The 27-year-old man was arrested in Parliament Street, junction with Parliament Square, by armed officers from the Met's Specialist Firearms Command.
He was arrested on suspicion of possession of an offensive weapon and on suspicion of the commission, preparation and instigation of acts of terrorism. Knives have been recovered from him.
He is being detained under the Terrorism Act and is in custody in a south London police station.
Detectives from the Counter Terrorism Command are continuing their investigation, and as a result of this arrest there is no immediate known threat.
An area around Whitehall near the Treasury building was closed following the arrest, and armed police were seen in the streets.
A witness told BuzzFeed News he had seen a man being held against the wall by armed officers.
"On the floor was a backpack with knives falling out of it," said Luke William, 28, from Southampton, who was driving through Westminster at the time. "Lots of police, lots of traffic, as you can imagine."
The arrest came on the day that prorogation takes place in parliament, marking the end of the parliamentary session. Most MPs were not in the Commons today, but many members of the House of Lords were present.
Security has been increased in Westminster following last month's deadly attack in which Khalid Masood killed five people before being shot dead by armed police.
Matthew Champion is a deputy world news editor for BuzzFeed News and is based in London.
Contact Matthew Champion at firstname.lastname@example.org.
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