Yesterday, a police spokeswoman confirmed said five people had serious injuries but it was believed six people were involved.
About 90 minutes later, she said two of those had been updated to critical injuries and two people have been airlifted to Waikato Hospital.
In a statement, police said helicopters had been dispatched and diversions were in place.
Fire and Emergency New Zealand also sent crews to the crash, shift manager Paul Radden said.
He said there were two people trapped in separate cars and crews from Maketu and Pukehina used rescue equipment to remove them from the vehicles.
Waka Kōtahi New Zealand Transport Agency had closed the road between Pongakawa School Rd and Benner Rd in Pongakawa but it has since reopened.
A St John spokeswoman confirmed there were six patients involved in the crash with a mixture of moderate to serious injuries.
Three helicopters and three ambulances were sent to the scene.
St John received a call at 3.59pm, she said.
