The reopening of the Manawatu Gorge has been delayed because the structural damage on State Highway 3 is worse than expected.
Photo: NZTA
The road was due to reopen this week but is likely to remain closed for another week.
That would allow a concrete retaining wall to be replaced.
Engineers only spotted that the wall near the Ashhurst turn-off had shifted, when slip debris was cleared off it.
The Transport Agency said heavy rain yesterday meant it was too unstable to even allow one lane to reopen in the meantime.
The road - which connects Palmerston North to the East Coast of the North Island - was closed by a large slip nearly a month ago, but a second slip earlier this month delayed contractors working to clear the debris.
It is the third time in six years the road has been closed for an extended period because of slips.
The closure means motorists have to take the winding Saddle Road to get to Hawke's Bay, adding an hour to the trip.