The Karangahake Gorge between Tauranga and Auckland is set to close over two days during set hours later this month.
New Zealand Transport Agency Waka Kotahi said the closure of State Highway 2 would occur on Monday, March 30 and Tuesday, March 31 between 9am and 3pm.
"We need to carry out urgent repairs to a retaining wall which runs from the road into the river," a spokesperson said.
"Over time, cavities have formed under the wall’s foundations. Crews have filled these gaps and now need to place large rocks in front of the wall to secure the base.
"Repairs are very dependent on the weather and reasonably low river levels."
A 50-tonne crane would be needed for the works, which a single-lane closure would not provide enough room for.
NZTA said the work also needed to be done during the day so divers could safely guide rocks into place.
"We chose these closure times to avoid school and commuter peaks and allow freight to move in the morning and afternoon."
Contractors would also use the closure to progress storm-related repairs in the Karangahake Gorge.
The work is expected to continue under stop/go traffic management until May.
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