Police were called to the incident, which involved two cars, at the intersection of the highway and Kauri Point Rd near Tahawai at 8.44am.
Senior Sergeant Glenn Saunders said one person had been critically hurt in the crash and two others had moderate injuries, and all were being transferred to hospital.
"The Serious Crash Unit is on its way to the scene and as a result, the road has been closed in both directions and is likely to remain shut for several hours," Saunders said.