The road between Kawakawa and Paihia will be closed for at least a fortnight weeks after a massive slip.
The winding hill road road is the main tourist route to the Bay of Islands.
Tonnes of earth came down on State Highway 11 at Lemons Hill during yesterday's deluge in the Far North, shunting a car sideways.
The occupants escaped unhurt.
The Transport Agency (NZTA) says the 80-metre-long slip was unstable and it would take two weeks to make the hillside safe enough to re-open the road.
NZTA spokesman Steve Mutton said the timing would be dependent on the weather.
"It's fine right now, but there have been days of heavy rain and more is forecast next week. More rain could potentially see the slip start to move again," he said.
Engineers would be using a drone to survey the extent of the slip, Mr Mutton said.
In the meantime, traffic heading north to Paihia would have go by State Highway 10, adding about 20 minutes to the trip.
All other State Highways in Northland are open and crews are out checking roads for potholes and other road damage caused by surface flooding in recent days.