Constable Darrin Low, of Hampden, said the occupants of a four-wheel-drive vehicle were lucky to be alive after a two-tonne boat was dislodged from the vehicle's trailer and caused the car to smash into a steep grass verge on Saturday.
''A southbound car towing a trailer and a boat has hit a bump and, for whatever reason, the boat has disconnected and the car has fishtailed.''
Const Low said the vehicle and trailer fishtailed for 150m until they rolled into the side verge.
''From what I can see here, you have got a two and a-half to three-tonne boat and a two-tonne car - once the boat started to sway, the driver was never going to be able to hold on to that.''
He would ask NZTA to assess the bump and the bridge as soon as possible, he said.
He said one man with back injuries and another with a broken arm were flown to Dunedin Hospital, and two others were taken by ambulance to Oamaru Hospital with ''bumps and bruises''.
The driver escaped uninjured.
State Highway 1 was closed for 15 minutes while ambulance and fire crews assessed the injured occupants.
He said the occupants, four teenagers and a man in his 60s, all from Waikouaiti, were all wearing seat belts.
''That's probably what saved them. They were very lucky.''
