The man, reported to be a local swimmer, was bitten on his right leg by a shark as he swam between The Pass and Clarkes beach.
New South Wales police said he was seen floating in shallow water, close to the shore line, and dragged onto the beach.
An ambulance was called and he was pronounced dead a short time later.
Beaches in the area have been closed for 24 hours and people are being warned to stay out of the water.
“At 10.45am, police and paramedics were called to Main Beach after reports of a shark attack,” NSW police said in a statement. “Inquiries into the identity of the deceased, and what he was doing in the water at the time of the incident, are continuing.”
The beach was not supervised at the time of the attack as seasonal duties don’t start until next week.
“As the official patrol season does not start until 20 September beaches are not currently patrolled in Byron Bay but at council’s request, lifeguards will be on duty for at least the next 24hrs ensuring the water remains clear from Belongil Beach to Tallows Beach across Byron Shire Council,” Surf Lifesaving Australia said in a statement.
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