A van carrying seven people rolled over a bank in a crash south of Charleston, near Westport.
Emergency services were called out at 2.31pm after the van had rolled 10m down a bank on State Highway 6 about 10km south of Charleston, Southern fire communications duty manager Brent Dunn said.
Police said all passengers were out of the van and there were no fatalities.
A St John ambulance communications advisor Ian Henderson confirmed two ambulances and two rescue helicopters from Nelson and Greymouth attended the scene.
Mr Henderson said one patient was transported via helicopter to Nelson Hospital with serious injuries.
Another was taken to Greymouth Hospital with moderate injuries.
The remaining four patients had minor injuries or were uninjured.
The road was closed to one lane and delays should be expected, police said.