The vehicle hit a power pole on Paddon Rd, a narrow rural gravel road at Branxholme, about 20km northwest of Invercargill, and rolled on to its side.
Senior Sergeant Darryl Lennane, of the Southern District Command Centre, said there was only one occupant in the vehicle, and no other vehicles were involved.
Nearby houses were plunged into darkness when power was cut off while firefighters extricated the man.
Ryal Bush Transport manager Shannon McEwan confirmed the injured man was one of his drivers.
He had picked up a load of gravel from a nearby gravel pit and was driving north.
New Zealand Fire Service Southern communication centre shift manager Brent Dunn said the call came in for the crash at 3.35pm.
The crash resulted in what he described as a ''heavy entrapment'' - the man was trapped in the wreckage of the truck, and another truck with a crane on the back, plus a digger, had to be brought in to extricate him.
The driver was removed from the crashed truck at 7.13pm.
Sergeant Brent Kingsland, of Invercargill, said at the scene the driver had leg injuries, which he did not believe were life-threatening.
Firefighters attended from Wallacetown and Winton, along with police and St John.
