Locket Road in Wealdstone is currently cordoned off by police following a stabbing shortly after 6:15pm.
The road is blocked in both directions with a police cordon outside a parade of shops in Wealdstone High Street.
Members of the public can be seen gathering around the junction of the High Street and Locket Road.
The 186 bus route is on diversion.
A spokesperson for London Ambulance Service said: “We were called at 6.14pm yesterday (10 August) to reports of a stabbing on Wealdstone High Street, Harrow.
“We sent a number of resources to the scene including an ambulance crew, an incident response officer and a medic in a fast response car. We also dispatched London’s Air Ambulance.
“We treated a patient at the scene and took them as a priority to a major trauma centre.”
Met Police told Harrow Online: “Police were called by LAS at 18:17hrs on Wednesday, 10 August to High Street Wealdstone, after reports of a stabbing.
“Police attended with London’s Air Ambulance.
“A man was found with stab injuries. We await an assessment of his condition.
“A crime scene is in place and enquiries are ongoing. One male arrested has been arrested in connection with the incident.”
If you have a news story for Harrow Online, please WhatsApp us on 07999 293 922.