"Police were called about 5pm. Initial reports are there have been injuries."
NZTA said the road was expected to be closed for 3-4 hours as the police undertake a serious crash investigation.
A northbound detour via SH16 from Silverdale was put in place, the agency said.
A photo of the scene just after 5pm showed a collision involving multiple vehicles spread across both the north and southbound lanes.
Lines of traffic could be seen forming.
A northbound motorist in the area said traffic was backed up at least a kilometre after the crash.
He said it looked like a ute and a car were involved in the crash.