A rockfall has closed State Highway 6 west of Murchison.
Vehicles were initially trapped by the slip at Dellows Bluff which sent giant rocks plummeting on to the road, but all have since been released, Waka Kotahi said.
The highway between the SH65 intersection and Hinehaka Road was closed to all traffic while the slip was investigated, and contractors were making sure the road was safe to be used.
The transport agency is urging motorists to delay their journey if possible, as the only alternative route for people driving from Christchurch to Nelson is via State Highway 1 which will add an hour to travel times.
Waka Kotahi will provide a further update after midday.
Slip on SH5 between Napier and Taupō
A dropout on State Highway 5 between Napier and Taupō will take about 10 weeks to fix.
The dropout, which is nearly 200m long, is between the rural areas of Te Haroto and Tarawera.
This part of the road has been down to one lane for nearly two weeks, and soil erosion around the area has only got worse with heavy rain.
Waka Kotahi Hawke's Bay system manager Martin Colditz said a buttress would be built against the cliff face to help fix the problem.
"The first step will be to cut an access-track halfway down and create staging for a digger. This will enable us to carry out the backfilling works without the need for anyone working at the bottom of the site."