The driver, John Liew, from Singapore, said he saw an animal on the road, which he thought was a squirrel, and braked. The rental people-mover ran into loose gravel and overturned.
First on the scene were Justin and Jodie Chittock, from Waimate, who helped pull the family out and called emergency services.
Mr Liew said the group was heading for Lake Tekapo to attend the wedding of his younger brother on Saturday afternoon.
The groom's parents were among those in the overturned vehicle.