A St John spokesman said that two people suffered seriuos injuries and were flown to Timaru hospital while two others were taken in with moderate and minor injuries.
Two rescue helicopters - one from Christchurch and another from Dunedin - were sent and flew four people to Timaru Hospital.
A police spokeswoman said emergency services were alerted at 4.45pm to the crash on Mt Cook Rd at Ben Ohau.