The single-vehicle crash occurred in Airedale Rd about 10.40am when a northbound white station wagon failed to take a slight right bend.
Acting Sergeant Paul Alden, of Oamaru, said the vehicle came into contact with gravel which caused the driver to lose control.
The driver then overcorrected and the vehicle flipped before it came to rest upside down in a ditch.
The two occupants, a male and a female, both of Oamaru, were not injured.
-By Daniel Birchfield