The road will remain closed at least for another hour. Diversions are in place for traffic heading in both directions.
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 pyschologically 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."
At the scene this afternoon, a red sheet was placed over half of the mangled wreck.
Cordons shut the stretch of road off from motorists, with diversions in place at Te Mahanga Rd and Te Aute Trust Rd.
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 busses 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.