Police said the collision took place on the A264 Dorking Road at 6.50pm on Friday (August 12), 800 metres away from the Great Daux roundabout and the A24 junction.
A spokesman for Sussex Police said a purple Ford Fiesta and a black Audi TT, travelling westbound, collided. The Fiesta was also in collision with a white Fiat 500 travelling eastbound.
A 21-year-old woman, from Horsham, who was a passenger in the Fiesta, sustained serious injuries.
She was airlifted to Southampton General Hospital by the Air Ambulance with critical injuries, the spokesman added.
A 24-year-old man, who was driving the Fiesta, along with a 34-year-old man, driving the Audi, and a 60-year-old man, driving the Fiat, sustained minor injuries, police said.
A 55-year-old woman, who was a passenger in the Fiat, also sustained slight injuries. All four were from Horsham and were treated at the Royal Sussex County Hospital, in Brighton.
Road policing officer Sergeant Alan Spicer, said: “We’d like to hear from anyone who saw what happened or noticed any of the cars prior to the crash.
“And in particular we’re keen to trace the driver of a red car travelling west towards Great Daux roundabout who could be an important witness.”
The A264 was closed to until 2.45am while emergency services dealt with the incident.
Any witnesses or anyone who may have other information is asked to email [email protected] or phone 101, quoting Operation Beckton.
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