Traffic is closed both directions of the Castlereagh Highway between Dunedoo and Mendooran following a serious two-vehicle crash this morning.

Emergency services and the Crash Investigation Unit are on the scene.

Motorists are being advised to avoid the area, use diversions and allow extra time for travel.

Westbound traffic has been diverted along the Golden Highway to Dubbo, then up the Newell Hwy to Gilgandra, then the Castlereagh Highway to Mendooran.

Eastbound traffic is the same in reverse: along the Castlereagh Highway to the Newell, then Golden, highways.

This diversion is suitable for all vehicles, according to Live Traffic NSW.