One person has been seriously injured and three others rushed to hospital after a crash on the North Circular in Neasden.
An air ambulance has landed in North West London after a collision involving at least three cars and a lorry at just after 12.30pm.
The A406 North Circular Road is closed westbound at the junction of Neasden Lane, with traffic building up beyond Brent Cross Flyover.
Traffic is also moving slowly eastbound on the A406.
The road will be closed for a few hours to allow emergency services to operate. An air ambulance earlier landed on the slip road.
Traffic is being diverted through Neasden, Dollis Hill, Willesden and Wembley.
Bus routes 112,232,332 are also being diverted.
A statement from London Ambulance Service said: “We assessed and treated a total of nine patients and we were able to discharge five of those at the scene.
“We took four patients to hospital, one of whom was very seriously injured.”
Four people were taken to hospital and one person was ‘very seriously injured’ in the crash, London Ambulance Service (LAS) has confirmed.