Two cars collided tonight on State Highway 1 on the southern side of the Brynderwyn Hill south of Whangarei.
Two people with serious injuries were cut out of the wreckage by the Fire Service.
The Transport Agency said traffic was being diverted while police at the scene investigated the crash.
Agency spokesman Anthony Frith warned motorists that the diversions would add at least 30 to 40 minutes to their travel times.
He said southbound traffic should turn off at Waipu and travel down the coastal road to Mangawhai, and northbound traffic should take State Highway 12 through Maungaturoto towards Dargaville, then State Highway 14 to Whangarei.
