Police want to talk to the driver of a red car travelling on the A264 Dorking Road at Horsham when a serious crash happened there on Friday evening.
It left a 21-year-old woman critically injured and it has since emerged that two other people suffered serious injuries in the crash, say police.
Police were called to the scene, around 800 metres east of the Great Daux roundabout and the A264’s junction with the A24, at 6.51pm.
All the people involved in the crash came from addresses in Horsham, say police.
A spokesman said a purple Ford Fiesta and a black Audi TT travelling west collided, and the Fiesta was then also in collision with an eastbound white Fiat 500.
A passenger in the Fiesta, a 21-year-old woman, suffered serious injuries.
She was airlifted to Southampton General Hospital by the Kent, Surrey and Sussex air ambulance where she remains in a critical condition.
The Fiesta driver, a man aged 24, sustained chest and shoulder injuries and was taken by ambulance to the Royal Sussex County Hospital, Brighton.
A 55-year-old woman, who was a passenger in the Fiat, suffered injuries to her right foot, chest and abdomen and was also taken to the RSCH.
The Audi driver, a man aged 34, and the Fiat driver, a man aged 60, both sustained slight injuries for which they were treated at the hospital.
Road policing officer Sergeant Alan Spicer, said: “I’d like to repeat an appeal for anyone who saw the crash, or who noticed any of the cars just beforehand
“And in particular we’re keen to trace the driver of a red car travelling west towards Great Daux who we believe could be an important witness.”
The A264 was closed to traffic until 2.45am while emergency services dealt with the incident.
Any witnesses or anyone who may have other information is asked to email firstname.lastname@example.org or phone 101, quoting Operation Beckton.