The road remains closed as police and other emergency services complete a scene examination and remove the two vehicles.
Cordons were in place shutting the stretch of road off from motorists. There were diversions in place at Te Mahanga Rd and Te Aute Trust Rd.
Emmerson Transport managing director Ian Emmerson confirmed the truck involved was one of theirs.
He said the driver was as good as could be given the situation.
"He's uninjured, but psychologically he's affected.
"The driver will be supported. Whatever support he needs, we'll give him."
Mr Emmerson said they felt for the families involved. "You don't wish that upon anyone."
Cars, trucks and school buses were driving on the road before cordons were set up and were drawn to a stand still.
Uniformed students piled out of the buses and waited on the side of the road in 27C heat.
Motorists started doing u-turns as police officers advised of a delay that could be as long as five hours.
A number of trucks had to reverse some 200m back up the road as they were too big to complete a u-turn.
The road will be closed for some time and motorists are urged to avoid the area or delay travel plans.
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