“One person died at the scene.
“The road is expected to remain closed for some time, and diversions are in place.”
Motorists were advised to avoid the area.
Fire and Emergency was called at 1.51am and sent two appliances from Whanganui, central shift manager Murray Dunbar said.
Crews had helped with “extrication” and left the scene with police and ambulance officers, he said.
Hato Hone St John attended the crash around 1.50am, sending two transporting ambulances and taking one patient to Whanganui Base Hospital in a moderate condition, a spokesman said.
The Herald has requested further comment from police.
The NZ Transport Agency said SH3 was closed between Kai Iwi Valley Rd and Watt Livingstone Rd, with a detour in place.
Road users were advised to delay their journeys or use an alternate route, the agency’s website said.