Sunrise Balloons said the hour-long trip near Queenstown had been uneventful and was operating within normal wind speeds when the pilot attempted to land on a private airstrip just before 10am.
“On approach, the balloon was caught by a sudden wind gust and the basket containing passengers impacted with a low bank,” the company said in a statement.
Medics said that the injured people were scattered over an area the length of a football field.
“So responding to those patients, and understanding what the situation was, took some time based on the length of the scene,” David Baillie, an operations manager for St John Ambulance, told TVNZ.
The balloon basket ended up near a driveway while the balloon fabric was draped over a powerline, according to the company.
The two seriously injured passengers were taken by helicopter to Dunedin Hospital. The pilot and the eight other passengers were treated for minor or moderate injuries and later released.
Sunrise Balloons owner and chief pilot Hugh McLellan said the company was “deeply upset” about the incident and the injuries sustained to their pilot and guests.
The company said it has temporarily stopped further flights and is cooperating with police and aviation authorities, who are investigating the incident.
All the passengers were New Zealand residents, the company said. New Zealand closed its borders to foreign tourists more than a year ago due to the coronavirus pandemic.