A young man has suffered suspected spinal injuries after falling eight metres through a roof on a worksite on Sydney's northern outskirts.

The 26-year-old fell eight metres onto timber scaffolding at a property in Kenthurst about 2pm, injuring his head, shoulder and leg.

CareFlight's Rapid Response Helicopter joined with NSW Ambulance paramedics to provide initial treatment.

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It took an hour for paramedics, Fire and Rescue NSW and the Rural Fire Service to extricate the man.

After he was freed, CareFlight's specialist doctor performed a clinical assessment and ultrasound.

He was taken by ambulance in a stable condition to Royal North Shore Hospital.

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