A helicopter near the scene of the crash. Photo: Linda Robertson
A police spokesman said State Highway 1 at Titri, just north of Waihola, was blocked after a truck and trailer unit rolled.
Emergency services were called to the scene, between Titri and Bungards roads, at about 11.55am.
"One person has critical injuries and the road will remain closed while a scene examination is carried out and the vehicle is cleared," the spokesman said.
Diversions are in place but motorists are advised to expect delays.
