A 12-year-old boy suffered serious head, abdominal and leg injuries in a three-vehicle road smash near Atiamuri.
The boy was one of two people airlifted to Waikato Hospital after the serious crash on SH1 south of Atiamuri.
The crash happened about 2pm yesterday near the Ohakuri Rd turnoff, halfway between Taupo and Tokoroa.
Police believed a car had crossed the centre line before hitting the side of a horse float truck.
Senior Sergeant Fane Troy, of Taupo police, said the driver seemed to have lost control before crashing head-on with a second vehicle, travelling behind the truck.
Mr Troy said there were three occupants in one car and one person in the other car.
Taupo's Greenlea Rescue Helicopter arrived shortly before 3pm and was there for about 20 minutes before taking the 12-year-old boy to Waikato Hospital with severe head, abdominal and leg injuries.
Mr Troy said a second rescue helicopter was also called to take another crash victim to Waikato Hospital.
He said the two others involved suffered minor injuries and were able to walk away from the crash.
A Waikato Hospital spokeswoman said two crash victims were being treated in the emergency department yesterday afternoon. She said one was in a serious condition and the other was in a stable condition.
The horse float, which was carrying live horses, had minimal damage. The driver, George Potts, said he was driving up the hill towards Tokoroa when he quickly swerved to miss a car going the other way.
"I looked behind me and saw cars all over the place,'' he said.
When The Daily Post arrived about 3pm the road was blocked with a diversion put in place by police.
The road reopened about two hours after the crash.