"The incident occurred just before 4.25 this afternoon," a NSW Ambulance spokesperson told the Macleay Argus.

Police were told the man was attacked by a shark while surfing.

He was helped from the water and treated by paramedics for a serious arm injury.

Three NSW Ambulance crews and the Westpac Rescue Helicopter Service were on scene with a critical care doctor and critical care paramedic dispatched.

"Much praise must be given to bystanders who helped the man from the water and provided that crucial initial first aid," NSW Ambulance Inspector Andrew Beverley said.

"It was a significant bite and the man suffered serious injuries to his arm as a result.

"He was stabilised on scene and then flown to John Hunter Hospital in a serious but stable condition."

"It might be cold at the moment but it's important to always be aware of your surrounding in the water, even in winter."

Officers from Mid North Coast Police District will liaise with the Department of Primary Industry to investigate the circumstances surrounding the incident.

The popular beach has been closed by Surf Life Saving NSW.

Surf Life Saving NSW drones will assist with surveillance flights for sharks in the area at first light.

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