Acting Sergeant Norm Wallace of Kapiti police said the northbound truck left State Highway 1, near the Kebbell Drive intersection, and drove through scrub, down a small bank and hit a concrete anchor before stopping about 3m from railway lines.
The man, a single occupant of the truck, was taken to Waikanae Park before being airlifted to Wellington Hospital with serious injuries via the Westpac Rescue Helicopter.
The Serious Crash Unit was investigating.
CRASH: #SH1 Waikanae not blocking at the intersection of Kebbell Drive. #TakeCare and expect delays if you are heading northbound. ^MN