Police are still investigating a crash in Herbert after emergency services were called to the single-vehicle crash in Otepopo St, on Saturday.
One person was flown to Burwood Hospital and another was taken by ambulance to Oamaru Hospital. Two passengers were unhurt.
Sergeant Blair Wilkinson, of Oamaru, said the vehicle had rolled and crashed into a ditch.
He said all four men were from Ashburton.
A 22-year-old passenger was flown to Burwood Hospital, in Christchurch, with back injuries, and the 19-year-old driver was transported to Oamaru Hospital with minor back injuries.
The 20- and 25-year-old passengers were both uninjured, Sgt Wilkinson said.
A St John spokeswoman confirmed one helicopter and two ambulances attended.
Sgt Wilkinson said police were awaiting a blood sample to find out whether impairment was a factor.
