Belongil Beach and Main Beach at Byron Bay have been closed for 24 hours after a shark attacked a surfer in the early hours of this morning.

NSW Police say that emergency services were called to Manfred Street in Byron Bay at approximately 6.40am after reports that a man had been bitten on the upper left thigh.

The 41-year-old Suffolk Park man returned to the beach with his board after the attack, and alerted other surfers to the presence of a shark.

He was treated at the scene by paramedics, and then airlifted to Gold Coast University Hospital, with his condition described as serious but stable.

Westpac Life Saver Rescue Helicopter has completed an extensive search of the coastline off Byron Bay and Belongil Beach this morning, sighting dolphins and turtles in the nearby waters, but no sharks.

It is unclear what species of shark attacked the man, but marine biologists from the NSW Department of Primary Industries are working together with law enforcement to find out more.

Beach-goers are urged to follow safety advice from Surf Life Saving NSW and by visiting the Department of Primary Industry’s website and the SharkSmart app.

Image: Getty Images / Education Images / UIG