A woman is in hospital in a critical condition after an incident on the North Circular Road on Monday lunchtime.
The incident, which took place on the westbound carriageway, involved another driver and saw the victim - who had been in a car herself - struck by a vehicle.
One witness told this newspaper he had heard "a blood-curdling scream" during the incident.
The as-yet-unnamed woman was airlifted to hospital where she remains.
A Scotland Yard spokesperson said: "Police were called at approximately 11:50hrs on Monday, 20 January following reports of an altercation between the occupants of two vehicles at Henlys Corner, NW11.
"During the altercation a woman was struck by a car. The car then left the scene.
"London Ambulance Service and London's Air Ambulance attended the scene and the woman was taken to a central London hospital for treatment; she remains there in a critical condition."
Just under an hour later, the police stopped a car in Islington and arrested a man on suspicion of attempted murder - he remains in custody.
Clary Nelson, who lives in Beaufort Drive near to the scene, told this newspaper: "I had done a night shift last night, so I'm half awake, but I heard this blood-curdling scream from a woman - bearing in mind the scene is probably about 200 metres away.
"I immediately thought it was a woman being stabbed, and I looked out and saw it happening, saw a number of men running towards what was going on."
Clary added that he could see someone on the floor and a car "parked diagonally" across the carriageway. He said it appeared that an elderly man and woman had both got out of their car after a traffic incident before being allegedly assaulted by another man.
"When I saw her they [paramedics] were pumping her chest, I really hope she has come around now," he said. "She was pretty bad."
Police enquiries are ongoing and road closures on the North Circular Road are still in place,
This page is being updated.
Did you see what happened? Contact Sam on the newsdesk using 02074330120 or Sam.Volpe@Archant.co.uk
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