A man has been arrested on suspicion of grievous bodily harm and assault, and under the Terrorism Act, after two police officers were injured outside Buckingham Palace.
The Metropolitan Police tweeted to say the officers suffered minor injuries to their arms while detaining a man with a large knife after they had spotted it in his car.
They said they stopped the man at around 8.35pm.
London Ambulance Service treated both injured officers and neither needed hospital attention, police added.
No one else was injured. Police gave no more detail about the man.
According to the BBC, a Palace spokesman said summer opening hours and tours would go ahead over the weekend, adding that it will be “business as usual”.
A police cordon remains in place.
On Twitter, photos and video were published on Friday night showing a big cordon near the palace, which witnesses said was later widened, and a crowd of people watching.
The suspect was taken to hospital for treatment of minor injuries and was then taken to a police station for questioning.
Detective Superintendent Guy Collings said: “A man in his mid-twenties has been arrested by police after they spotted a weapon inside his car.
“The quick and brave actions of both officers meant that the suspect was detained very quickly. No members of the public had any interaction with this individual at the scene.
“He will now be questioned by detectives in police custody. It is too early in this investigation to speculate any further.”
Witness Nicole Kyle told the BBC: “I was walking toward The Mall and St James’s Park when I saw police rush down toward the palace in great numbers.
“As we got further down The Mall we saw armed police outside a police van, at which point we were able to walk closer to the palace still, where we were eventually stopped by a cordon.
“All we were told was that there’s been an incident.
“A few minutes later police came by to have us clear the area and move further away from the palace.”
No members of the Royal family were at the Palace when the incident took place.