A shark mauled a surfer off an ocean beach in Sydney in the Australian city's third shark attack in two days, authorities have said.
The surfer, believed to be in his 20s, was in a critical condition in hospital with serious leg injuries after the attack at a northern Sydney beach, police said.
"The man was pulled from the water by members of the public who commenced first aid before the arrival of emergency services," New South Wales state police said in a statement.
All of Sydney's northern beaches were closed until further notice.
The attack at North Steyne Beach in the suburb of Manly came hours after a shark bit a large chunk out of a young surfer's board about 4km north along the coast at Dee Why Point.
That surfer, reportedly a boy aged about 11, was uninjured but the beach was closed immediately.
Yesterday, a large shark bit a 12-year-old boy on the leg as he played with friends at a beach in Sydney harbour, leaving him fighting for survival in hospital.
The boy and his friends were jumping from a 6m rock into the water off Shark Beach in the eastern suburb of Vaucluse when the predator struck, police said.
"It was a horrendous scene at the time when police attended. We believe it was something like a bull shark that attacked the lower limbs of that boy," said Superintendent Joseph McNulty, New South Wales marine area police commander.
"That boy is fighting for his life now," he told reporters today.
Recent heavy rain had drained into the harbour, and authorities believed the combination of the brackish seawater and the children's splashing created a "perfect storm" for a shark attack, Supt McNulty said.
He warned people not to go swimming in the harbour or other river systems in New South Wales because of the risks.
He praised the boy's "brave" young friends for pulling him out of the water.
Officers put the unconscious child in a police boat and gave him first aid, applying two tourniquets to stem the bleeding from his legs, Supt McNulty said.
The boy was in intensive care at Sydney Children's Hospital surrounded by family and friends, Supt McNulty said.
There have been more than 1,280 shark incidents around Australia since 1791, of which more than 250 resulted in death, according to a database of the predators' encounters with humans.
Increasingly crowded waters and rising ocean temperatures that appear to be influencing sharks' migratory patterns may be contributing to a rise in attacks despite overfishing depleting some species, scientists say.
A great white shark mauled a man to death as he surfed at a popular northern Sydney ocean beach in September last year. Two months later, a bull shark killed a woman swimming off a remote beach north of Sydney.
