A surfer is in critical condition after being bitten by a shark on Sydney’s Northern Beaches – marking the city’s third shark attack in 26 hours as authorities order widespread beach closures.

The man, aged in his 20s, suffered serious lower leg injuries after being bitten at North Steyne Beach in Manly about 6.20pm on Monday.

New footage shows the man being dragged from the water by other beachgoers who performed first aid until paramedics arrived.

First responders treated the man on the sand before he was rushed to the 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,’ NSW Police said in a statement.

A 15cm bite mark on the young surfer’s board suggests he was most likely attacked by a bull shark, according to shark biologists from the primary industries department.

Northern Beaches Council lifeguards sounded the alarm immediately after the attack, then erected shark warning signs and dispatched a jet ski to patrol the water. Surf Life Saving NSW also launched a drone to assist with locating the shark but there have been no further sightings.

‘Council lifeguards will continue to patrol for the remainder of the day and tomorrow,’ a Northern Beaches Council spokesperson said.

A young man has been attacked by a shark at Manly Beach and rushed to hospital

Emergency services were called to the beach about 6.20pm Monday

New footage from the latest attack shows the man being dragged from the water by other beachgoers who performed first aid until paramedics arrived

It is the third shark attack in 26 hours in Sydney. A boy aged 12, a boy aged 11 and the man in his 20s were targeted

It’s the third shark attack in Sydney in 26 hours with experts saying peak season for bull sharks in the Sydney area is January and February.

On Monday morning, an 11-year-old boy was thrown off his surfboard by a large shark, believed to be a bull shark.

It took several bites out of his board at Dee Why Point.

The shark net had been set as normal on Dee Why Beach, which was closed at the time of attack because of large swells and dangerous surf.

The attack followed another off Shark Beach, Vaucluse, about 4.20pm on Sunday afternoon.

A boy, 12, was swimming with his friends at a popular jump rock to the west of the beach and was bitten outside the netted swimming area.

His friends helped him to shore.

It’s believed he was also attacked by a large bull shark.

The man suffered serious injuries after being bitten on the leg at Manly and was helped by bystanders before paramedics arrived

A 15cm bite mark was found on the young surfer’s board (pictured), indicating he was most likely attacked by a bull shark

Quick thinking beachgoers provided first aid to the surfer

The man, believed to be in his 20s, was rushed to the Royal North Shore Hospital in a critical condition

Manly Beach has been closed following the attack

Lifeguards put up signs at Manly. Authorities have ordered widespread beach closures

Police on Monday urged people not to swim in murky, low-visibility water after bucketing rain drenched Sydney and its surroundings at the weekend.

Extra fresh water in the harbour after recent heavy rain, combined with the splashing effect from people jumping off a rock face, created a ‘perfect storm’ for Sunday’s shark attack, Superintendent Joseph McNulty said.

‘I would recommend not swimming in the harbour or our other river systems across NSW at this time,’ he told reporters before the Dee Why incident was reported.

Heavy swell has also prevented the operation of smart drumlines, which notify authorities of shark activity along most of the NSW coast since Sunday.