A school-run crash is causing heavy delays to traffic in areas of Burnt Oak and Mill Hill.
Police closed the northbound carriageway of the A41 Watford Way after the collision involving five cars and a pedestrian near the junction with Weymouth Avenue at 2.50pm.
London Ambulance Service was also called to the incident but no-one was seriously injured.
One lane remains closed while police wait for one of the cars, a BMW estate, to be recovered.
Paramedics are still at the scene and an ambulance service spokesman said a 24-year-old man has been treated for back pain.
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