State Highway 2 was closed overnight after extensive rain caused a slip.
The slip on SH2 between Napier and Wairoa known as The Devil's Elbow came down around 1pm yesterday and closed the highway overnight.
New Zealand Transport Agency regional highways manager Chuck Dowdell said experts could detect the slip was still unstable.
"Our geotech experts have detected further movement in the slip, so in the interests of safety, we need to wait until things settle down before we can start work clearing it."
Mr Dowdell said that the only alternative route between Napier and Wairoa is via SH5 and then down SH2 through the Waioeka Gorge, or the reverse.