British police have arrested a man on Whitehall, the street home to numerous government ministries in central London, and recovered knives.
The man was detained on terrorism charges, police said following the incident on Thursday.
Police said no one had been injured in the incident close to Prime Minister Theresa May's official Downing Street residence in Westminster.
Ms May was not at Downing Street at the time of the incident, her spokesman said.
The incident comes just over a month after a British-born convert to Islam ploughed a car into pedestrians on nearby Westminster Bridge killing four people before stabbing to death a police officer in the grounds of parliament.
A Reuters photographer saw at least three knives on the ground after a man was arrested on Whitehall, a street in central London where many ministries are located.
Armed officers sealed off the area.
A Reuters reporter and photographer saw police holding a dark-skinned, bearded man dressed in a hooded, black coat.
His right hand appeared to have a bandage wrapped around it.