A Waka Kotahi NZ Transport Agency spokesperson said the slip, between Kaikoura and Ward near the intersection with Kiwa Rd, occurred about noon on Thursday and forced it to close SH1 just after 1pm.
Several large trees overhanging the road were threatening to fall and must be removed before it can safely reopen.
Motorists will face delays this afternoon while the slip is cleared, the spokesperson said.
There are alternative routes inland to Waiau for drivers already south of Kaikōura, closer to Peketa, or through the Lewis Pass (SH7) via Waipara.
People already north of the slip should take SH63, the Wairau Valley route from Blenheim to St Arnaud, then onto Waipara/Christchurch via SH65, the Shenandoah highway.
"The large, overhanging trees above the road have been de-stabilised by the slip and will need to be removed before the road can re-open. This could take several hours this afternoon."
Road users are encouraged to take other routes between Picton and Christchurch today and overnight for certainty:
- SH7 the Lewis Pass via Waipara if people are setting out from Christchurch.
- If already in Kaikōura, the inland route to Waiau then onto SH7, (from Peketa on SH1), the Lewis Pass.
- If north of the slip site near Blenheim, the Wairau Valley SH63 route connects to the Lewis Pass via SH65.
