Police are investigating the suspicious death of a woman at Narrabri, who was found unconscious on a road on New Year's Eve.

About 10pm (AEDT) on Monday, police located the 43-year-old woman lying unconscious on Peel Street, Narrabri, in northern NSW. She had severe head injuries.

The woman was treated at Narrabri Hospital before being airlifted to Sydney in a critical condition, where she died late on Wednesday.

The death is considered suspicious and has been referred to the coroner.

Police investigations continue.