A man has been knifed in one of central London's busiest hotspots, as police scrambled to Trafalgar Square.
The force said emergency services were called at 9.10pm.
Photos from the scene showed a very heavy police presence, as multiple police cars gathered.
Officers confirmed the incident is not being treated as terrorism.
The victim's condition was later confirmed as non life-threatening by police.
At least five squad cars and two police vans attended, as well as the London Ambulance Service - and large sections of the square was taped off.
In a statement, the Metropolitan Police said: “Police were called at 9.11pm on Wednesday, 21 August to Trafalgar Square Westminster following reports of a stabbing.
“Officers attended with LAS.
"A male [no further details] was found suffering from stab injuries.
“A crime scene and road closures are in place. Motorists advised to avoid the area.
"This is not being treated as terrorism and initial inquires indicate that the victim and suspect maybe known to each other.
— GlobalRaceCollective (@globalracers)August 21, 2019
“No arrests at this early stage; enquiries continue.”
Alexander Zakharenko tweeted some footage of the scene with the words: "What's going on on Trafalgar Square..."
The clip shows the square thronged with police cars and officers moving bystanders back.
Any witnesses or those with information that could assist police are asked to call 101 ref CAD 7777/21 Aug.