The victim of the horrific shark attack at North Steyne Beach in Manly has been identified as local musician, Andre de Ruyter.

The surfer, from Wollongong south of Sydney, was pulled from the water by onlookers around 6.20pm on Monday night after he sustained catastrophic injuries to his lower legs.

By the time paramedics arrived on scene, Mr de Ruyter was already in cardiac arrest and was given CPR on the stand.

Mr de Ruyter received emergency surgery at Royal North Shore Hospital on Monday, where he remains in a critical condition following the attack that left him with severe shark bites on his legs.

“We had our inspector liaising with the aero-med team, and what they do is liaise with our hospitals. So there was (blood) that actually came from the northern beaches, and Royal North Shore,” Ms Marks said.

“We had two police highway patrol cars that met at (the) Spit Bridge, and then what they said (it) was almost like an F1 pit stop of 10 seconds or less and they just opened the door, and they administered 13 units of blood”.

She said that fellow surfers and beachgoers raced to help Mr de Ruyter, and surf lifesavers applied a tourniquet before emergency services arrived, which helped save his life.

A bull shark is believed to be behind the attack.

Authorities warn that recent coastal weather has created conditions that attract shark activity, as four separate shark incidents have occurred across NSW in less than 48 hours.

A 39-year-old man has been taken to hospital with minor injuries following a shark attack at Point Plomer, near Port Macquarie.

The shark involved is believed to also be a bull shark.

On Monday morning, a young surfer was shaken after a shark had taken a bite out of his surfboard at Dee Why beach.

Another boy was attacked near Shark Beach, Vaucluse, at 4.20pm on Sunday, about 20km away from the Dee Why attack.

The 12-year-old is now fighting for life in Sydney’s Children’s Hospital.

Authorities believe a bull shark was also behind Sunday’s attack.

Steven Pearce, CEO of Surf Life Saving NSW, warned people to stay out of the water.

“Do not enter the water for swimming or surfing for the next 48 hours. This is unprecedented. To have this in the 24 hours,” he said on Sunrise on Tuesday morning.

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