The driver of a vehicle that flipped on State Highway 2 on Tuesday afternoon had fallen asleep behind the wheel, endangering their own and other road users' lives, senior sergeant Nathan Davis of Tararua police says.

Police attended the accident - which occurred as the vehicle was travelling north on the highway, just south of Matamau - after being advised by St John ambulance.

"The driver had fallen asleep, failed to take the corner and left the road," Mr Davis said.

"The driver and other road users are extremely lucky there were no other vehicles on that piece of busy road and police are urging all road users to take some time in the planning of their intended travel, consider the previous day's events and how much sleep they've had.

"Drivers need to consider how far they intend to travel and ensure they consider quality breaks, stay hydrated and focused."

Mr Davis said it's important to drive to the conditions, slow down and take care.

The driver was taken to Palmerston North Hospital for treatment and observation.

Investigations into the accident are continuing.