A 64-year-old man is fighting for his life after he was knocked down by a quad bike in south London.
The pedestrian was struck by the vehicle in Sutton late on Thursday evening, police said.
Two people riding on the quad bike, a male driver in his 20s and a pillion passenger, were taken to hospital with minor injuries.
Police and paramedics were called to London Road, Hackbridge at around 11.20pm. The pedestrian was then taken to hospital where he remains in a critical condition.
A Scotland Yard spokesman said no arrests have been made.
Officers from the Met's Serious Collision Investigation Unit are investigating the incident and have appealed for information.
Contact officers from the Serious Collision Investigation Unit at Merton on 020 8543 5157 with any information.