A couple were into their second of a five day hike on Boundary Creek World National Trail in the Washpool National Park when a 45-year-old woman fell down a cliff face onto rocks and logs and was seriously injured.

Police, ambulance and national parks crews arrived at the scene around 3.30pm that afternoon. Police described the area as very steep rugged country, only accessible on foot.

The initial plan was to winch her out of the densely forested area, but the Westpac helicopter, which arrived around 7.30pm, was unable to overcome heavy fog and low cloud.

Instead emergency services carried her out of the National Park on a stokes rescue litter.

The Westpac helicopter landed at a nearby property and the critical care medical team was rushed to the scene by four-wheel-drive. NSW Ambulance paramedics and the helicopter crew treated the lady for possible serious head and spinal injuries and she was then flown to the Princess Alexandria Hospital in Brisbane.

The woman was in a serious condition at the time.

She is now in a critical but stable condition at the hospital's intensive care unit.

Helicopter crews reported the task was drawn out due to the location and terrain, they arrived back at base in the early hours of Tuesday morning. Police said they were on duty until 11.00pm.

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