This is the dramatic moment a critically wounded shark attack victim was treated by helicopter paramedics in Australia.

The male victim, 27, was surfing off North Steyne Beach in Manly, New South Wales, when a shark reportedly bit his leg on January 19.

The shark, believed to be an aggressive bull shark, tore off a chunk of his right calf before lifeguards pulled the unconscious man out of the water.

He had reportedly lost a significant amount of blood and went into cardiac arrest before intensive care paramedics arrived on a Toll NSW Ambulance Rescue Helicopter.

Footage shows medical staff landing on the shore yards away from where the victim was lying with a mangled right calf. They resuscitated him before rushing him to Royal North Shore Hospital, where he is fighting for his life.

In a statement, the New South Wales police said: 'The man, believed to be aged in his 20's, was treated for serious leg injuries by NSW Ambulance paramedics and taken to Royal North Shore Hospital in a critical condition.

'All beaches on the Northern Beaches are closed until further notice, and this will be reviewed on an ongoing basis.'

The incident is the third of four shark attacks off the coast of Sydney within 48 hours.

On Sunday, a boy, 12, was left in critical condition after being bitten near Nielsen Park.

On Monday, an 11-year-old surfer was attacked by a shark at Dee Why. While on Tuesday, a 39-year-old man suffered minor injuries when a shark bit through his surfboard at Crescent Head.

Authorities said the consecutive attacks occurred after days of heavy rain, which can attract sharks closer to shore as runoff flushes nutrients into the water.

Officials said the exact shark species involved is not yet clear, but believe notoriously aggressive bull sharks to be the culprits.

Steve Pearce, chief of the rescue service Surf Life Saving NSW, said: 'If anyone's thinking of heading into the surf this morning, anywhere along the northern beaches, think again.

'We have such poor water quality that's conducive to bull shark activity. We have two people critically injured in hospital this morning. Just go to a local pool, because at this stage, we're advising that the beaches are unsafe.'

Bull sharks are large, aggressive sharks known for their ability to live in both saltwater and freshwater. They are considered one of the most dangerous shark species to humans due to their size, strength, and unpredictable behaviour.