Emergency services are responding to a digger on fire on the back of a truck, which closed State Highway 1 south of Cambridge.
The fire is between Karapiro and Piarere, just south of the Horahora Bridge, near Becks Nurseries.
SH1 has been reopened to one lane working under a Stop-Go system.
Waikato police Senior Sergeant Paul Slater urged people to avoid the area or keep their eyes on the road instead of rubbernecking at the fire.
The NZ Transport Agency is asking people to follow the directions of emergency services, and is warning people to expect delays.
Fire and Emergency NZ were called to the fire on Tirau Rd (State Highway 1) about 11.30am, and police were called not long after, a police spokeswoman said.