Beachgoers dragged a badly injured swimmer from the water after she was mauled by a shark at one of Australia's most popular beaches on Saturday, police said.Four people have been killed in an unusual spate of shark attacks around Australia this year.Police said the woman in her 30s was in critical condition after she was "bitten by a shark" off Coogee Beach in Sydney."The woman was pulled from the water by members of the public who commenced first aid before the arrival of emergency services," police said.The woman suffered serious injuries to her arms and legs, they added.A shark-spotting helicopter buzzed over the beach in the aftermath, while jetskis were dispatched to patrol the sea for signs of the predator. A string of beaches along Sydney's eastern coast were closed as a precaution. Coogee is one of Australia's most beloved beaches and is a popular spot for tourists.Australian scientists believe increasingly crowded waters and rising ocean temperatures are shifting sharks' migratory patterns, which may be contributing to a rise in attacks.A 12-year-old boy died after he was bitten by a shark while swimming in Sydney Harbour in January.Three divers were fatally mauled in separate incidents between May and June -- two in Western Australia and the third in Queensland.There have been nearly 1,300 shark incidents around Australia since 1791, of which more than 260 resulted in death, according to a database of shark encounters with humans.