The section of highway was damaged during last year's Cyclone Gabrielle, and had been closed for repairs since mid-February.
The critical Northland highway was due to fully reopen on the 13 May.
NZTA Waka Kotahi says there was a slip over the weekend and it has continued moving over the last couple of days.
A substantial amount of material fell on Tuesday, it said.
The agency said it was still in the early stages of assessing the best solution, and would confirm more details as soon as it could.
RNZ