A Met spokesperson said: “Police were called at 09.34am on Tuesday, 14 April to reports of an altercation outside Brent Cross Shopping Centre, NW4.
“Officers attended with the London Ambulance Service, and a man in his 50s was taken to hospital, where he remains, with a stab wound.
“Police remain in the area, with support from the National Police Air Service, and are working to locate a suspect who was seen leaving the scene.
“No arrests have been made at this time. A crime scene is in place. It is believed to be an isolated incident.”
A London Ambulance Service spokesperson said: “We were called at 9.33am today (14 April) to reports of a stabbing in Brent Cross Shopping Centre, NW4.
“We sent an ambulance crew, a paramedic in a fast response car, an advanced paramedic and an incident response officer to the scene.
“We treated a patient at the scene and took him to a major trauma centre as a priority.”