A significant washout closed State Highway 1 in the Far North yesterday afternoon, and motorists are warned that there is no alternative route and the road could be closed until the middle of next week.

State Highway One damage in Cape Reinga. Source: Troy denison

The highway is currently closed between Whaler Road and Lamb Road south of Pukenui in the Far North.

"There is no alternative route. Motorists will not be able to travel north to Pukenui and on to Cape Reinga or south from there to Kaitaia. Motorists are advised to delay their journeys in the Far North," the New Zealand Transport Agency said.

Work is underway to divert the stream and place new rock and material to build up a base for a new road.

This involves laying multiple think steel pipes and then backfilling with material to bring it up to road level, as the washout is more than four metres deep.

"There is a significant workforce and heavy lifting equipment on site and we are working to have one lane open to traffic as soon as possible but that is unlikely to be before the middle of next week," the NZTA said in a statement.

"More rain is forecast for the region so that may affect progress. When the lane is opened it will operate with stop/go traffic management in place.

There have been suggestions from some that unsealed forest roads or Ninety Mile Beach could be used as alternative routes, but the Transport Agency has warned drivers those routes could be dangerous.

"The Transport Agency and Far North District Council do not support suggestions that motorists can drive on 90 Mile Beach or on unsealed private roads through the forest to get around the washout," the agency's Northland system manager Jacqui Hori-Hoult said.

"These are high risk options for drivers and their vehicles if they are not experienced at driving in these conditions.

"We don't want local services being diverted to rescuing vehicles stuck in the sand or searching for people lost or broken down in the forest.

"Please do not use these routes."

Civil Defence, emergency services and local authorities were working on a plan to support those affected, she said.

State Highway One damage in Cape Reinga. Source: Troy Denison