State Highway 27 is closed near Tatuanui, Matamata-Piako District following a crash between two trucks.
Police were called to the crash at the intersection with Cussen Road at 11.30am.
Both drivers received serious injuries and have been flown to Waikato Hospital, says a police spokesperson.
"One of the trucks was carrying a large concrete block and removing it from the road will take some time.
"Diversions are in place. Police ask that motorists are patient if they experience delays.