The incident happened in Northolt Road at around 4pm yesterday (March 5).
Officers and London Ambulance Service crews attended and found the boy who had been stabbed.
#Harrow, London
Something major happened in South Harrow as more then 5 police vehicle are following serious incident.More then 5-6 shops have been cordoned including bus stop.
Video shot by me @ravindraJourno pic.twitter.com/vCroNhpHOC
— Ravinder Singh🇬🇧 (@ravindraJourno) March 5, 2025
He was taken to hospital where his condition was assessed as life threatening.
Two 16-year-old boys were also found injured nearby.
They were also taken to hospital, however, they have since been discharged.
A number of crime scenes are in place and officers remain in the area.
A 16-year-old boy was arrested overnight on suspicion of grievous bodily harm and taken into police custody.
A spokesperson for Metropolitan Police said: “Officers were called to a reported altercation outside an address in Northolt Road, Harrow at 16:00hrs on Wednesday, 5 March.
“Two 16-year-old boys and one 15-year-old boy were stabbed in the incident.
“The three victims received treatment at the scene from the London Ambulance Service and were transferred to hospital.
“The 15-year-old boy remains there in a life-threatening condition. The other boys have been discharged.
“A 16-year-old boy was arrested overnight on suspicion of grievous bodily harm and taken into police custody. Enquiries are ongoing and a scene remains in place.”
