State Highway 2 through the Karangahake Gorge will close overnight on Wednesday to allow repair work to be carried out.
The road which is between Paeroa and Waihi will close from 9pm through to about 3am on Thursday.
Contractors will be blasting an overhanging rock from above the road in the gorge.
NZTA said the road will open as soon as debris has been cleared, possibly down to a single lane.
There will be cordons at Paeroa and Waitawheta Bridge.
Alternative routes are via SH27/29 over the Kaimai Range, or via SH25/25A, the Kopu-Hikuai Road.
NZTA is urging motorists to make sure they are through the gorge before 9pm and to [www.journeys.nzta.govt.nz/traffic/regions/3 check on the NZTA website] before attempting to travel in the area.