Three teenagers are in hospital with life-threatening injuries, and a fourth with serious injuries, after their car collided with a lorry.
Two 18-year-old women and two males, aged 18 and 16, were in the Vauxhall Corsa when the accident happened on Saturday afternoon in West Sussex.
Four air ambulances attended the scene of the crash, in Wisborough Green.
The three most seriously injured teenagers were flown to hospitals in London and Essex.
The fourth was taken to Worthing Hospital.
The 71-year-old driver of the 7.5 tonne flatbed lorry was unhurt, Sussex Police said.
Both carriageways of the A272 Billingshurst Road were closed for four hours while emergency services were at the scene of the accident, at the junction of Kirdford Road and Loxwood Road.
Sussex Police are appealing for witnesses to come forward.