The vehicle had gone off State Highway 6 near Benmore, north of Winton, about 12.30pm, a Fire and Emergency New Zealand spokesman said.
The vehicle crashed into a power pole, and ''multiple lines'' had come down, covering the car and the road, he said.
A St John spokeswoman said the driver of the vehicle was taken to Southland Hospital with serious injuries, but had no further information.
Diversions were put in place by police, and the road was opened to one lane from about 2pm.