The Manawatu Gorge, which has been plagued by several massive slips, will be closed on Wednesday while contractors use explosives to blast large rocks in the area.
The gorge, State Highway 3, will be closed from 9am to 4pm and diversions will be in place, New Zealand Transport Agency (NZTA) says.
Contractors will blast large "stubborn" rocks that came down in a slip earlier this year which caused damage to a nearby bridge.
The rocks will be blown into smaller pieces and removed.
The gorge was closed about 15 months ago after the first of several massive slips came down on the highway.
It was reopened in both directions in September, but some small sections are still down to one lane and controlled by traffic lights.
NZTA hopes work on the road will be done by the end of November.