Sergeant Blair Wilkinson, of Oamaru, said a 74 year old woman fell asleep while driving south in her Daihatsu vehicle, veered off State Highway 1 and hit a power pole about 10.30am.
The crash occurred between Hilderthorpe Rd and Macdonalds Rd.
The Invercargill woman was taken to Oamaru Hospital with minor injuries.
Following the crash, SH1 was reduced to one lane for about half an hour before it was closed and a detour put in place as repairs were made to the power pole.
Police inquiries were continuing, Sgt Wilkinson said.