The road remains shut from Pohlen Rd to Peria Rd and will remain closed for some time while the Serious Crash Unit investigates.
Motorists are asked to avoid the area if at all possible as there will be delays.
The NZ Transport Agency tweeted that there is an official detour in place, via Waharoa East Rd. This detour will only add another 5-10 minutes to your journey.
A nearby resident on SH27 said he provided assistance at the crash scene after he went to check that his neighbour's cattle had not escaped.
"The car was upside down in the ditch. It had gone through some rails and landed in the drain," he said.
"I gave a bit of assistance while I was there. I helped get a couple of young kiddies out of the car and a gentleman. I then held up a cover until the fire brigade got there to keep them in the shade."
He was not aware of the cause of the crash, but said the children's grandparents were following in a separate vehicle when the crash happened.
