A washout has closed State Highway 1, 40 kilometres north of Kaitaia.
The road is the only route to Cape Reinga.
The Transport Agency said the damage was significant and the highway would remain closed over the weekend.
With no alternative route, motorists can't travel north to Pukenui and on to the Cape, or south from Pukenui to Kaitaia.
The agency said it was working closely with Civil Defence, emergency services and local authorities on a response to support those in the area who might be affected.