An 11-year-old girl was killed while waiting with her mother at a bus stop when a pensioner's car veered on to the pavement and crashed into them.
Officers were called to The Common in Stanmore, following reports that a vehicle had collided with two pedestrians and a stationary bus.
Emergency services pronounced the girl dead at the scene, while her 46-year-old mother was taken to hospital and remains in a critical condition.
Firemen cut the 69-year-old driver from her Ford Fiesta and she was taken to hospital with minor injuries. No arrests have been made.
Police said they were awaiting formal identification ahead of a post-mortem due to take place tomorrow at Northwick Park Hospital.An inquest is expected to open at Barnet Coroner's Court "in due course", Scotland Yard said.