A woman in her 20s has died after crashing into a tree off the Castlereagh Highway Monday night 22 December.

A passing motorist saw the crashed vehicle near Mendooran and reported the scene to emergency services.

Passers-by assisted the driver, however, the woman died at the scene.

Emergency services were called to the site, around 9.15pm.

Officers attached to Orana Mid Western Police District will prepare a report for the information of the coroner.

NSW Police is urging anyone with information to contact Crime Stoppers.