State Highway 65 is down to one lane between Springs Junction and Murchison, in the Buller District, after a truck rolled this morning.
No-one was injured when the truck rolled at about 4am, but cranes are needed to remove the vehicle.
While the crash scene is being cleared, the highway will be down to one lane with stop/go signs used to control traffic.
The road is not expected to fully reopen before 5pm.
Police would like to thank motorists in advance for their patience and advise anyone planning to travel on this route to allow extra time for their journey.
ENDS
Issued by Police Media Centre