A "serious incident" has closed a section of SH1 between Puhoi and Orewa heading south to Auckland at the start of the school holidays.
The NZ Transport Agency says the section of motorway between the Waiwera off-ramp and Grand Drive is closed and motorists are advised to follow the directions of emergency services and allow extra time for their journey.
The agency described the event as a "serious incident".
Police said one person was seriously injured and had been taken to hospital after the "incident".
"The serious crash unit is in attendance and police are currently making enquiries to establish exactly what has occurred," a statement said.
Motorists are being asking to take a detour route by exiting the motorway at the Hibiscus Coast Highway, turning right onto Grand Drive, then turning left to rejoin SH1 at the Orewa on-ramp.
Heavy vehicles must detour to the Silverdale on-ramp because of heavy vehicle restrictions on Grand Drive.