A woman in her 20s has been shot by police and four other people arrested in an anti-terror operation in north-west London and Kent, Scotland Yard says.
Officers said the operation was not connected to the earlier arrest of a man near Parliament.
The woman was one of the subjects of the investigation and is in a serious but stable condition.
Two men, 20 and 16, and another woman, 20, were held after the Willesden shooting and a 43-year-old woman was arrested in Kent.
Police said they were arrested on suspicion of the commission, preparation and instigation of terrorist acts.
They were in custody at a south London police station.
The woman was shot after armed officers entered an address in Harlesden Road, Willesden, shortly before 7pm Thursday (UK time).
A police spokesman said she was taken to hospital by ambulance.
"Due to her condition, she has not been arrested at this time and remains under police guard at hospital," he said.
"The address and persons connected with it had been under observation by counter-terrorism officers as part of an ongoing intelligence-led operation."
Searches at the locations of the arrests were ongoing, as well as further searches at "linked addresses" in London, police added.
The incident has been referred to the Independent Police Complaints Commission and the Met's Directorate of Professional Standards, as is procedure.
Meanwhile, video reported to have been taken at the moment of the shooting has been posted on social media. It appears to show armed police surrounding a terraced house as five shots rang out.