One person was cut from a vehicle by fire crews following a crash at Dome Valley, north of Auckland.
A police spokesman said they were called just after 3.30pm, and told a car was against a barrier on State Highway 1, and a second car was facing the wrong way.
He said it was understood an elderly woman was in one of the cars but it was unclear if she required medical attention, or if there were other injuries.
Ambulance and fire crews are at the scene.
SH1 is now closed between Warkworth and Wellsford, and diversions are in place.
North-bound traffic should travel via Kaipara Flats Rd, Carran Rd, Woodcocks Rd and SH16.
Southbound traffic should travel via Sh16, West Coast Rd, Woodcocks Rd and SH1.