A man has been stabbed in London's Trafalgar Square, the Met Police said.
Emergency Services were called at 9.11pm on Wednesday evening following reports of a knife attack.
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.
The victim, who has not been identified, was found suffering from stab injuries, the Met said.
The incident is not being treated as terrorism, and initial inquiries indicate that the victim and the suspect may be known to each other.
The man's injuries are not life-threatening, officers say.
The Metropolitan Police tweeted: "The victim stabbed in #TrafalgarSquare #Westminster his injuries are not life threatening. No arrests have been made at this stage, inquires continue."
Trafalgar Square is one of London's busiest tourist hot spots, and is the site of the National Portrait Gallery and St Martin-in-the-Fields church.
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.
Another onlooker posted: "Something's going down in Trafalgar Square ... 8 police and ambulance. All roped off. Hope no-one badly hurt."
The Met said: "A crime scene and road closures are in place. Motorists advised to avoid the area.
"No arrests at this early stage; inquiries continue."
