Police are appealing for witnesses following a collision between a cyclist and a car in Northolt.
It happened shortly before 0530 this morning on Church Road, opposite the junction with Eskdale Avenue.
The cyclist, a 30-year-old woman, was taken to a central London hospital suffering a head injury. Her condition is described as serious but stable.
The driver of the car stopped at the scene. She and her female passenger were taken to a west London hospital as a precaution.
Officers from the Serious Collision Investigation Unit are investigating.
Any witnesses are asked to call 020 8991 9555.