The Manawatu Gorge is closed after a tanker carrying blood supplies hit a rock and is hanging off a guard rail.
Police said the front of the tanker is suspended over the river and a crane was on its way to try to lift it back on to the road.
It is believed the driver escaped uninjured.
In other parts of the North Island, roads are closed because of snow and ice.
The Rimutaka Hill Road is closed, as is State Highway 1 on the Desert Road and between Taihape and Waiouru.
State Highway 49 to Ohakune, and State Highway 4 from Tohunga Junction toward National Park, are also shut.
Police are urging people not to travel on central North Island roads tonight, saying driving conditions are poor.