The bus and cab of the truck were shunted about 50m into a paddock while the trailer tipped on the road.
Eastern Bay of Plenty Police said the injured were being treated in Rotorua, Tauranga and Whakatane hospitals.
An 8-year-old was listed as a status one in Rotorua Hospital and a 6-year-old was listed as a status two in Rotorua Hospital.
They were transferred to Rotorua Hospital by helicopter.
The truck driver was also taken to Tauranga Hospital by helicopter. He was initially thought to be in a critical condition but was now stable. He would remain in hospital overnight for observation, police said.
"The bus was carrying students from Trident and Whakatane High Schools, and primary school students from Taneatua. Due to the number of different schools involved, we are still confirming the numbers of students on the bus," Eastern Bay of Plenty Area Commander Inspector Sandra Venables said.
However, all of the children were from the Ruatoki Valley area.
Youthtown rescue helicopter pilot Nat Every told APNZ the scene was one of chaos, with injured children and upset adults strewn around the paddock where the two vehicles had come to rest.
"It's really one of those accidents that you certainly hope you don't have to attend very often," he said.
Justin Allan, company director of Transbay Coaches which owns the school bus, said it appeared the logging truck had slammed into the back of the bus when it pulled over to drop children off at a stop.
The bus had been operating on the route for many years without any problems, he said.
"We're pretty shaken up about the whole thing."
As the news spread to the close-knit Ruatoki community, family members began to arrive at the scene, many of them distressed.
Students sat on a blue tarpaulin until they were taken away in order of priority by emergency services.
Ms Venables said police thanked the local community for their help and support following the crash.
"Many members of the local community were on the scene immediately and responded quickly to provide first aid and assistance. It is a very close-knit community and their efforts this afternoon were remarkable and much appreciated by all emergency services."
Trident High School board of trustees chairman Peter Foster said the school was still trying to make contact with some students.
He said the school's principal and other teachers had gone to Whakatane Hospital to visit injured students.
"Our hearts go out to the parents and families of the kids who have been injured."
He had phoned the homes of students he believed would have been on the bus and learnt that one had a broken leg.
He could not get hold of others and said they were probably at the hospital.
The Bay of Plenty Police Commercial Vehicle Investigation Unit have commenced their investigation at the scene and the area remains cordoned."
Ms Venables said the cause of the crash was not yet known and it was too early to speculate.
"Our focus now is working with the families and whnau of those who were injured and impacted by the crash, as well as on the crash investigation itself," she said.
- With Rotorua Daily Post
