State Highway 2 between Carterton and Greytown in the Wairarapa is closed following a crash earlier today.
A car collided with a tree at 11.20am.
The driver, the sole occupant of the car, has been airlifted to Wellington Hospital in a critical condition.
The road remains closed while the Serious Crash Unit examines the crash scene.
Motorists in the area are asked to delay travel or take alternative routes wherever possible.