Two police officers have been taken to hospital after being stabbed in central London.
The stabbing happened near Leicester Square at 6am and is not being treated as a terrorist attack.
Their injuries are not life-threatening.
The Mayor of London, Sadiq Khan, described the attack as “absolutely horrific” at an “important time for our country”.
A man has been arrested on suspicion of grievous bodily harm and assault on an emergency worker, the Metropolitan Police say.
The stabbing happened near the Haymarket, between Leicester Square and Piccadilly Circus, which is home to many of London’s theaters and Chinatown.
Leicester Square, an area that is usually full of commuters and tourists, is almost completely inaccessible to British citizens.