The small leak from the truck was not dangerous, the Greerton hazmat team at the scene determined.
Northern Fire Communications shift manager Scott Ormond said they initially thought it might be a leak of an agricultural chemical but it turned out to be minor.
"We left the scene in the hands to police to clear up as there was no need for our expertise," he said.
The driver of the truck, who was trapped, was successfully rescued by the Matamata crew and was in a moderate condition heading to hospital, Mr Ormond said.
A member of the Greerton hazmat unit said the substance turned out to be a fertiliser, "it wasn't anything too nasty".
"We were just called in case it was something more serious," he said.
Update 2pm: The truck involved in a collision with a ute has leaked a small amount of liquid onto the road.
Emergency services were investigating the potential for danger.
A police spokeswoman said the truck, which had rolled onto its side, was cleared from the road but police were directing traffic around the scene.
A Waikato police Facebook post said the occupant of the car had received a head injury.
A truck is on its side and has collided with a ute on State Highway 29, Lower Kaimai.
Police and emergency services were called to SH29 near Hanga Rd and Rapurapu Rd around 1.20pm.
A police spokeswoman said it appeared one person was trapped but she was unsure of injuries.
The truck was blocking one lane and motorists travelling through the area could expect delays.