Two of the victims of four shark attacks in NSW within 48 hours have been identified as 27-year-old Andre De Ruyter and 12-year-old Nico Antic.

De Ruyter, a South Coast musician, remained in intensive care today after he was mauled by what was believed to be a bull shark while swimming at North Steyne Beach in Manly about 6.20pm yesterday.

The former Austinmer Surf Life Saving Club volunteer has undergone surgery to have his lower right leg amputated.

The 27-year-old was attacked by a shark yesterday at a beach in Manly. (Supplied)
Andre de Ruyter remains in hospital following the attack. (Supplied)

A group pulled the 27-year-old from the water and began first aid as they waited for emergency services to arrive.

Multiple services, including paramedics, intensive care ambulance, a helicopter and police, responded to the incident.

He was taken to Royal North Shore Hospital in a critical condition.

The South Coast musician is one of four shark attack victims in NSW in the past 48 hours. (Supplied)

Nico has been the youngest of the shark attack victims.

He was jumping off a rock face at Neilson Park near Shark Beach in Vaucluse on Sunday when he was attacked by what police believe was also a bull shark.

He is a nipper at the North Bondi Life Saving Club.

9News understands the 12-year-old remained on life support today at the Children’s Hospital in Randwick.

12-year-old Nico Antic was attacked by a shark in Vaucluse on Sunday. (Nine)

The NSW Department of Primary Industries says bull sharks are known to frequent Sydney Harbour, especially during warmer months, and can be found in shallow waterways.

Swimmers are advised to be careful, avoid beaches, and stay clear of low-visibility and murky water.

Beaches between Town Breach and Crescent Head have been closed in the wake of the four separate incidents.