A rescue was launched on Friday after extensive damage, caused by heavy rain, left more than 40 people stranded.
More than 320mm of rain fell within 48 hours, double the area's January average.
That turned gullies into waterfalls, overwhelmed and blocked culverts, and triggered widespread debris flows across the road.
Crews had worked throughout the weekend to clear the stretch between Mātāwai and Ōpōtiki.
However, the New Zealand Transport Agency said the situation is far more complex than first anticipated.
"Our crews are doing everything they safely can, but the sheer number of slips and continuing amount of debris falling mean this is a complex and challenging situation," he said.
"The safety of our crews will always come first."
Brady said it was estimated there were up to 40 slips in total, including four to eight larger ones.
"Given the scale of damage and uncertainty about the condition of the road underneath the debris, we expect the closure to extend well beyond a short-term response."
People are urged to delay travel where possible, or to allow time for the long detour via State Highway 35 or State Highway 5.
The detour is five hours longer than driving from Mātāwai and Ōpōtiki on State Highway 2.
The NZ Transport Agency will also continue to monitor and maintain the detour route to ensure it is safe and accessible.
