The other vehicle has gone down a bank and is sitting near the railway line. The occupants are out of the car and appear to have minor injuries.
A detour using local roads is available for cars/light vehicles.
There is no alternate route for heavy vehicles the NZTA said.
The Police Serious Crash Investigation Unit has been called to the site and the Transport Agency will update the status of the highway around 5 pm.
Police said shortly after 4pm that traffic was being diverted to St Leonards Drive between Pukeko and Tui streets.
"St Leonards Drive is down to one lane in places, with contractors providing assistance with traffic control.
"Delays are expected and police ask motorists to drive with care.''