It is believed the car crashed off the road and into the river. It appeared to be about three to four metres below the surface of the water. The weather conditions in the Haast area were said to be fine.
St John spokesman Gerard Campbell said a helicopter from Greymouth arrived at the scene about 8.30pm.
He said two people were uninjured and assessed at the scene and a male patient with moderate injuries is being flown to Greymouth Hospital.