The 26-year-old was bitten repeatedly on a leg as he dived near Hinchinbrook Island off the coast of Queensland state, Queensland Ambulance Service Supervisor Ange Timmins said.
His friends brought him by boat to the town of Cardwell where ambulance officers stopped his bleeding and stabilized his condition, Timmins said.
He was flown by helicopter in a critical condition 150 kilometers north to the Cairns Base Hospital, she said.
His friends thought the man was attacked by a bull or tiger shark, Timmins said.
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