Police have announced a $1m reward for any information on the suspicious death of 26-year-old Harmony Bryant, who died more than two decades ago.

The young woman was found lying critically injured in bushland near Ocean Drive in Bonny Hills, about 25km south of Port Macquarie on the morning of August 16, 2003.

She had suffered burns to 60 per cent of her body, a broken pelvis, fractured wrist and left arm and her car was found on fire about 200m from the roadway.

According to police, the evidence suggests Bryant fell from a cliff and was helped back to her car by an unknown person or persons.

She was taken to hospital and died over a month later as a result of her injuries.

Detectives found she had booked accommodation for two people at the Mid Pacific Caravan Park the day before she was found.

Her death was transferred to the homicide squad for investigation by the coroner in 2007.

Four years later, an inquest found Bryant had died from the burns at Bonny Hills, caused by a person or persons unknown.

The second person has never been identified and no one has been charged over her death despite many public appeals and a previous $100,000 reward announced in 2011.

Images: NSW Police