Senior Constable Mike Colligan said a gust of wind had picked up the caravan the couple were towing.
"There was nothing the lady could do."
The Omakau Fire Service was called to the accident just after 1.30pm on Saturday.
Police and a St John ambulance also attended but the couple did not need hospital treatment.
• Police said speed and alcohol were possible factors in a crash on the Owaka Highway on Saturday.
Constable Andrew Denny, of Balclutha police, said two people were flown to Dunedin hospital after the single-car crash about 10.15pm.
The car left the road and "rolled and rolled and rolled and rolled" near Awatiki Rd.
The driver, a 17-year-old man from Invercargill, received moderate injuries and his passenger received moderate to serious injuries.
No further details were available.
• In another incident, on Saturday afternoon, a man allegedly drove 46kmh over the speed limit while exceeding the legal breath-alcohol limit, with his 10-year-old daughter in the car.
Constable Denny said the car was pulled over near Waitahuna on SH8. The driver was charged with driving at excess speed and drink-driving.
A 55-year-old male also faces charges after allegedly driving at twice the legal limit in Balclutha on Saturday night.
Both men will appear in the Balclutha District Court on November 14.
