Emergency services were called to a two-car crash on State Highway 1 near Huntly about 12.45pm this afternoon.
Four people were injured, three with moderate and one with serious injuries. All have been transported to Waikato Hospital.
Fire services were called to the scene to administer first aid until emergency services arrived, Fire Northern Communications shift manager, Megan Ruru said.
Waikato Police District Command Centre Senior Sergeant Andrew O'Reilly said two cars had collided and two cars were blocking one lane. He said one lane was open and traffic was now flowing freely.
The NZTA have advised drivers to avoid the area if possible.