(BSS/AFP) - A shark bit a surfer Tuesday in an Australian state`s fourth attack recorded over the past 48 hours, authorities said.

The man was surfing on the Mid North Coast of New South Wales when he was bitten by what authorities believed to be a bull shark.

He escaped with "minor" injuries, Surf Life Saving New South Wales said.

"A surfer reported seeing a shark and emerged from the water with wounds on the lower part of his body. Any wounds are reported to be minor," the water safety body said in a statement.

The surfer was the fourth person attacked by a shark in New South Wales over the past 48 hours.

Two people were attacked while surfing on Sydney`s northern beaches on Monday.

In one of those attacks, a shark bit a man`s legs as he surfed at Manly, leaving him in a critical condition.

A few hours earlier, an 11-year-old boy escaped uninjured when a shark took a bite out his surfboard a little further north.

All of Sydney`s northern beaches have been closed until further notice.

On Sunday afternoon, a 12-year-old boy was seriously injured as he swam at a beach on Sydney Harbour.

"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 on Monday.

Scientists suggested recent heavy rain had attracted bull sharks to coastal areas where rivers emptied into the sea.

"Sharks, especially bulls, are drawn to freshwater flushes to feed on fish and dead animals as they drift down from rivers," said Culum Brown from Macquarie University.

"Given the incredible rainfall we have had of late, the risk of encountering sharks is high. Stay out of the water till it clears."