The male truck driver and a female passenger, both from Kaitaia, were treated for minor injuries at Tokoroa Hospital.
The highway was closed for several hours while police investigated and cleared the scene.
About 30km away, contractors assessing a forest area on State Highway 32 near Whakamaru found a car which had come off the road and appeared to have hit a tree about 10m down a bank.
Police at the scene said the car was believed to have been there for more than 24 hours.
Inside were a family from Whakamaru, two adults and three children. Police said the driver of the vehicle was
23-year-old Lisa Crowley. Her partner, Richard Melling, 37, was the front-seat passenger. In the back seat were
11-year-old Jordan Melling, 2-year-old Brody Crowley and a 3-week-old boy, who police said was yet to be named. The newborn was in a baby capsule.
Police described them as a "blended family'' with Ms Crowley being the mother of the youngest two children.
Shortly after the car was found, several police were on the stretch of State Highway 32 blocking the road to one lane.
The car, which was down a bank on a sweeping curve, could not be seen from the road and there was no obvious damage on the road to indicate a crash had happened.
Police and ambulance staff who were at the scene had to wait for the Fire Service to finish at the State Highway 1
crash before they could help remove the family's bodies from the car. The bodies were covered by a sheet or a tarpaulin to shield them from view.
While emergency services removed the bodies, the highway was closed and traffic had backed up for at least 1km.
Several of those stuck in the cordon were leaving their cars and talking to people around them. Many had no idea what had happened and one man said the incident was terribly sad, especially so close to Christmas.
Although they did not know what had happened, the mood among those waiting was sombre. The flashing lights
from the police, fire and ambulance vehicles could be seen from the back of the queued vehicles.
Police are now working to trace the movements of the family to establish when the crash occurred. The family
were last seen about 8pm on Sunday in Whakamaru.
A man who lived next door to the couple in Whakamuru, Ian Eggleton, said they had hosted other neighbours at their home on Saturday night.
Mr Eggleton said he heard them leaving with the children about 1am on Sunday.
Ms Crowley's parents live in nearby Mangakino and yesterday visited the house about 5pm, staying for an hour.
Red flowers had been placed on the gate.
Mr Melling had lived at the house for about eight years, while Ms Crowley moved in about four years ago.
Taupo police area commander Inspector Steve Bullock said the crashes were an absolute tragedy.
"A Christmas in ruins for a number of families and friends. Our hearts go out to them.''
Mr Bullock said it was not clear when the crash happened and police would like to hear from anyone who knew of
the family's movements between Sunday night and yesterday.
Mr Bullock this morning said the family had been living in Whakamaru for a number of years.
"They are well known in that small community. They have extended family in Taupo, Tokoroa and Mangakino, all townships nearby,'' he told Radio New Zealand.
"It's always a tragedy when a whole family passes like this, and especially close to Christmas, which is a time when we all reflect on our own lives and our own family. It is very traumatising for all involved.''
Mr Bullock said the focus of police inquiries was to establish exactly when the crash occurred.
"We do know that they were last seen at their own home at around 8pm on the Sunday night, so we're asking anyone with any information as to their whereabouts between then and Tuesday afternoon to contact the police immediately.''
Mr Bullock said from the direction of the crash, it appeared the family were returning home from the Tokoroa area.
The car appeared to have left the road and travelled several metres before it hit the tree. The wreckage could not be seen from the road.
Mr Bullock said the road was relatively straight with a moderate bend where the vehicle had left the road.
He said it was a busy road.
"However the nature of the crash was such that the vehicle had left the road without any visible signs, so users of the road could drive east and west without noticing the vehicle, and in fact that is what has happened.
"It was only that the forestry workers had actually left the road and were in the firebreak area when they observed the vehicle.''
Mr Bullock said the crash was a reminder just how quickly lives can change.
"They can change in an instant, and we just need to be reminded that on our roads, we need to be paying attention at all times, and we need to drive to the conditions and drive to our ability at all times.''
South Waikato Mayor Neil Sinclair said such loss of life was a total tragedy so close to Christmas.
He said people did not recognise how dangerous rural roads could be, adding that he would like the police to look seriously at dropping some speed limits in the region from 100km/h to 90km/h.
"I had been so pleased that our road toll had been particularly low so far this year.
"I cannot imagine what it would be like for their families.''
Anyone with information about either of the crashes should Contact Taupo police on (07) 378 6060.