It looked as if the vehicle had barrel-rolled down the beach, he said.
The Northland Rescue Helicopter landed on the beach about 7.30pm and flew the man to Middlemore Hospital, which specialises in spinal injuries. A spokeswoman said last night he was in a serious but stable condition in the hospital's intensive care unit.
More than 800 fishers from as far away as Italy are taking part in the Snapper Bonanza, believed to be one of the world's biggest surfcasting contests. Whoever lands the biggest snapper by 4.30pm today will take home at least $30,000. Prizegiving takes place at Waipapakauri Ramp, about 10km north of Kaitaia.
Accidents during the contest are rare but are reasonably common on Ninety Mile Beach. In a 2012 inquest into a fatal crash on the beach, Northland coroner Brandt Shortland said it was "inherently dangerous" with ever-changing conditions.