Police hunt man who raped 12-year-old girl after abducting her from NSW park.

A 12-year-old girl has been abducted and sexually assaulted during a five-hour ordeal in Newcastle.

The girl was walking through Hudson Park in the Newcastle suburb of Adamstown Heights just after 9.15am on Tuesday, when she was threatened with a knife by a man who sexually assaulted her, police said.

She was then forced into a red car and driven to bushland where she was sexually assaulted for several hours before being released at Kotara Railway Station just before 2.15pm.

Police were called when she returned home and the girl was taken to John Hunter Hospital for medical examination.

A crime scene was established at Hudson Park and forensically examined while Newcastle police and the Child Abuse and Sex Crimes Squad have commenced inquiries.

The man has been described to police as being of a solid/large build with brown hair.

Police are urging anyone who was in the Adamstown Heights area or anyone with information that may assist to contact Crime Stoppers.