Six people were injured in a crash during the annual London to Brighton Veteran Car Run.
The 1902 Benz was involved in a collision with three other cars at about 11:35 GMT at Reigate Hill, Surrey.
It had been taking part in the annual parade of vehicles dating back to the early 20th Century.
Two people from the Benz were taken to hospital with serious injuries.
Two other people travelling in the car were taken to hospital with minor injuries, said Surrey Police.
A Ford C-Max, a Mercedes-Benz GLE and a Fiat Fiorino were also involved in the crash.
Two passengers from the Ford were taken to hospital with minor injuries.
The Royal Automobile Club, which stages the veteran run, previously said it was the world's oldest motoring event.
It commemorates the Emancipation Run in 1896, celebrating the Locomotives on the Highway Act which raised the speed limit from 4mph to 14mph and abolished the requirement for vehicles to be preceded by a man on foot.
The Royal Automobile Club said it would be "conducting a thorough review to identify any lessons which can be learnt from this accident".