Police were called at 12:20pm on Sunday, 29 November to reports of a collision between a car and a woman riding a mobility scooter on Mawney Road in Havering.
Paramedics from the London Ambulance Service also attended the scene.
The woman, aged 93 years old, was treated at the scene before being taken to an east London hospital for treatment. She remains in a serious condition and her family has been informed.
Detectives from the Roads and Transport Policing Command are investigating and would like to speak with anyone who saw the collision.
The car driver stopped at the scene and is assisting police with their enquiries.
No arrests have been made and enquiries into the circumstances remain ongoing.
Anyone with information that could assist the investigation is asked to contact police on 020 8597 4874 or via 101 quoting reference Cad 3030/29Nov.