Shortly after the crash, one person was trapped inside their car.
A witness said multiple emergency vehicles were at the scene, including several police cars and fire engines.
A long line of traffic was now diverted on other travel routes while SH1 was closed.
Traffic is still heavy in the area, and police have thanked the public for their patience.
Motorists are urged to avoid the area and delay their travel if possible.
NZTA spokesman Mark Owen said detours would significantly increase travel times both north and south.
"There is a detour, but it's not suitable for heavy vehicles. So our caution to people is to please avoid travel through there if at all possible."
Owen said he didn't know how long the road would be closed, but the serious nature of the crash meant it was likely to be several hours.
"Please be mindful we are in winter now, and do drive to the conditions.
"We don't know the cause of this crash, but certainly with the colder temperatures we've got a risk of ice across the roading network, as well as slips coming down in the wet weather we've been having.
"We just advise people to drive with extra caution and be mindful of their stopping distances."
The Serious Crash Unit is now investigating.
