Shortly before 23:45hrs on Friday, 25 November, police were called by the London Ambulance Service (LAS) to a report of a vehicle in collision with a pedestrian near to Vauxhall Bus Station.
Officers arrived on scene and were informed by LAS that the female pedestrian had left the location prior to a full assessment of her injuries.
The woman informed paramedics that she did not require assistance and she walked south from Vauxhall Bus Station towards Wandsworth Road.
Following the initial assessment of her injuries, officers are concerned that the woman may have sustained life-threatening or life-changing injuries.
A search of the area and local hospitals was conducted but the woman has not been found.
She is described as white and aged around 20 years. She was wearing a black dress and had blood on her face and head, with a scarf wrapped round her head to cover her injury.
No other persons were reported to be injured and no arrests have been made.
Police are urging the injured woman, or anyone who may be able to identify her, to call police in Lambeth on 101.