Police said it was "mind-blowing" no-one died in the crash, which occurred on a closed road.
The accident occurred at 9pm on Wednesday on Jackson River Rd, but emergency services were not notified until just after midnight after one of the occupants walked for three hours to the Arawhata River bridge, where he was able to get a cellphone signal.
Seven firefighters, two St John staff, one nurse and local police attended, as did two rescue helicopters from Queenstown. One of the helicopters was sent back to Queenstown, while the other took the injured man to Dunedin Hospital.
Senior Sergeant Nathan Snell, of Greymouth, said the group had travelled well past the road closed sign before the driver lost control close to the Martyr Saddle — about 8km past the closure — and the vehicle rolled 15m into a creek.
The driver was ejected from the vehicle and the 4WD landed upright in the creek bed.
The injured man was moved out of the water into the back seat of the vehicle by his friends.
"He was pretty banged up," Snr Sgt Snell said.
"The fact there were no fatalities is mind-blowing."
A St John spokesman said one other person required hospital treatment. Police and firefighters remained at the scene until 5am.
The gravelled Jackson River Rd, which leads to Lake Ellery and the Cascade Valley, was closed by the Westland District Council due to severe storm damage earlier this year.
Police have requested a blood test from the driver as a part of their investigation.
— Greymouth Star
