A section of State Highway 1 at Moerewa's Turntable Hill damaged in last month's storm could take up to six weeks to fix.
The highway is still open to traffic in both directions but the passing lane and one shoulder have been closed since the storm.
The underslip, just downhill from Hautapu Rd, is about three metres in length, with a drop of about 2m.
The slope has destabilised for another 5m below the visible slip.
A New Zealand Transport Agency spokesman said design work to repair the underslip was in progress, with repairs expected to be complete in four to six weeks.
The slip was not as severe as the damage that occurred at SH1 south of Kawakawa and SH12 at Kaihu. Turntable Hill was one of about 15 sections of the Far North's state highway network damaged in last month's storm but still open to traffic. All were being progressively repaired.
Another much larger slip a few hundred metres further up Turntable Hill did not pose a hazard to traffic or road stability at this stage. NZTA staff would keep monitoring it.
Meanwhile, work continues to repair and re-open many local roads. Pipiwai Rd is so badly damaged a temporary bypass will have to be built around three slips. The total repair bill for council roads in the Far North is expected to top $30 million.