The incident happened in Carshalton High Street just after 2.40am today (October 13)
Police attended alongside the London Ambulance Service, who treated the man at the scene.
He was later taken to a major trauma centre, and his condition has been assessed as life-changing.
Carshalton High Street reopened just after 10.30am today, and enquiries are ongoing.
No arrests have been made as police enquiries continue.
A spokesperson for the Metropolitan Police said: “Police were called at 02:42hrs on Monday, 13 October to reports of a collision between a pedestrian and a vehicle on Carshalton High Street, Sutton.
“Officers attended, along with the London Ambulance Service, and a man in his 30s was taken to hospital.
“His condition is believed to be life-changing at this stage.
“The road is now reopened and enquiries are ongoing.
“No arrests have been made.”
A spokesperson for London Ambulance Service said: “We were called at 2.35am today (13 October) to reports of a road traffic collision on High Street, Carshalton.
“We sent an ambulance crew to the scene and treated a man before taking him to a major trauma centre.”
