Drivers down south are being warned they may face short delays after "significant river erosion" on the South Island's Lewis Pass between Murchison and Maruia.
The NZ Transport Agency says the erosion has reduced State Highway 65 to a single lane for a short period north of Spring Junction.
"The Maruia River has eroded the cliff face under the highway during the heavy rain at the end of May, undermining the guardrail and posts," says Andrew James, System Manager for the Transport Agency Top of the South.
"We have placed barriers along the riverside and installed traffic signals to manage single-lane traffic, while we consider repair strategies."
Motorists are advised to take extra care when driving the route.