A spokesman at the Springs Junction garage said at one stage about 30 cars were backed up and some trucks.
However, the trucks were going over the Rahu Saddle to Reefton, and the backlog had cleared by 11am.
The New Zealand Transport Agency said the detour route for south-bound traffic was State Highway 6 from Murchison then State Highway 69 to Reefton, and on to State Highway 7 to Springs Junction, and the reverse for north-bound traffic.
Journey manager Lee Wright said the detour was a long a very winding stretch of the Buller Gorge so "extreme caution is needed for all vehicles".
- Greymouth Star