One person is trapped in their vehicle with serious injuries after they collided with another vehicle on the Kaipara Coast Highway.
Police are at the scene of the crash, where a person is being cut out of their vehicle. They will be airlifted to hospital, a police spokesman said.
Emergency services were called about 8.30am to the crash, in the Tauhoa area between Kaukapakapa and Wellsford.
The Serious Crash Unit is in attendance, the police spokesman said. He did not have further information on whether anyone else was injured.
The NZ Transport Agency warned commuters to add 25 minutes to their journey for a detour.
State Highway 16 is closed in both directions between West Coast Rd and Tauhoa Rd, with cordons in place.
Northbound traffic is being diverted at West Coast Rd to travel via SH1 through Warkworth, while southbound traffic is being detoured from Wellsford in reverse. SH16 remains accessible between Wellsford and Tauhoa Rd.