Four people were taken to hospital following a multi-vehicle crash this afternoon.
The collision between four cars happened just before 12pm in Brockley Hill, Stanmore, at the junction with the A41.
A woman, believed to be in her 70s, was taken to the Royal London Hospital by London Air Ambulance for injuries to her chest and abdomen.
A 43-year-old man was taken by road to St Mary’s Hospital with head injuries and a 65-year-old woman, who was the driver in one of the vehicles, was taken to Barnet Hospital, also with head
The fourth person, a 48-year-old man, was taken to Watford General as a precaution.
Firefighters from Mill Hill and Wembley had to extract the four people from the cars, which closed the road in both directions.
Police say the road will remain closed as they carry out an investigation into the causes of the crash.