Emergency services were called to Hull River Heads boat ramp near Tully on the Cassowary Coast, in Queensland, just before noon on Sunday after reports that a 39-year-old had been attacked while swimming at Kennedy Shoal, a shallow reef used for recreational fishing and diving lying about 45 kilometres off the coast.
The man was retrieved from the water in a critical condition but died shortly after being met by an ambulance.
The type of shark involved has not been confirmed, though bull sharks and tiger sharks are known to be prevalent along the Great Barrier Reef. Queensland Police said a report would be prepared for the coroner on the "sudden and non-suspicious" death, and did not release the victim's identity.
The attack comes a week after Steven Mattaboni, 38, was killed while spearfishing near Perth in Western Australia. Mattaboni was bitten on his legs by a 4-metre white shark on 16 May while on the water surface about 80 metres from shore and 20 metres from his boat near Rottnest Island, a popular holiday destination.
Comment: Details of the earlier attack: Man dies after shark attack off holiday island in Australia