A man has sustained a serious injury after a shark took a "significant bite" out of his arm while he was surfing on the NSW mid north coast.
The man, believed to be aged in his 20s, was surfing at Crescent Head Beach on Monday 4:30pm when he was attacked.
He was helped out of the water, treated by paramedics and later airlifted to John Hunter Hospital in a serious but stable condition.
NSW Ambulance Inspector Andrew Beverley said the bystanders who helped the man from the water and provided "crucial initial first aid" should be praised.
"It was a significant bite and the man suffered serious injuries to his arm as a result," Mr Beverley said.
"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 will contact the Department of Primary Industry to investigate the circumstances surrounding the incident.
The beach has been closed by Surf Life Saving NSW.