Horror scenes have unfolded at a secluded beach on the NSW north coast after a man was mauled by a shark.

About 11am on Tuesday, emergency services were called to North Shore Beach at Port Macquarie, on the northern side of the Hastings River.

The man, aged 23, was reportedly in the water when he was bitten by a shark.

He was treated at the scene for leg injuries after multiple ambulance crews and a rescue helicopter raced to the scene.

The shark victim was transported to Port Macquarie Base Hospital in a critical but stable condition.

North Shore is a secluded open beach accessed by ferry from Port Macquarie and is popular for 4WD driving and beach fishing.