A bomb disposal unit was deployed to "investigate a silver car" in Battersea.
Police were called on Sunday (December 17) shortly before 1.40pm to report of a man who had collapsed in behind the wheel of a car in Prince of Wales Drive junction with Albert Bridge Road.
Witnesses described police officers shouting for people to stay in doors.
Roads around the area were closed as officers used a mechanical robot to conduct a search of the vehicle.
Upon searching the vehicle, an item was found by officers which was being treated as suspicious.
As a precaution, A3320 Prince of Wales Drive at the junction of Albert Bridge Road, A3031 Albert Bridge Road / Cambridge Road southbound, and A3220 Battersea Bridge Road were all closed for a short while.
Officers from the Metropolitan Police investigated the incident along with the London Ambulance Service.
The man has been taken to a central London hospital and police await an update on his condition.
Routes around parts of Chelsea, Belgravia and Battersea are heavily congested.
Bus routes 49, 170, 319 and 345 were also affected.
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