The Gwydir Highway is closed in both directions at Gibaltar Range – between Grafton and Glen Innes – due to a fallen tree.
As there is no suitable diversion, vehicles already on the road are being advised to park and wait.
Motorists not already in the area are being advised to delay their journey.
The closure will be in place until the tree is removed.
Traffic crews and emergency services are on scene.
For the latest traffic information, visit www.livetraffic.com, download the Live Traffic NSW app or call 132 701.