Shark attack victim Nico Antic has died in a Sydney hospital.

The 12-year-old was attacked by a suspected bull shark as he was jumping off a rock face at Neilson Park, near Shark Beach in Vaucluse, on Sunday.

The boy’s friends jumped into the water to pull him to safety, but Nico suffered serious leg wounds and was taken to hospital in a critical condition.

Young shark attack victim Nico Antic has died in hospital. (Nine)

READ MORE: Shark sighting at Manly forces closure of beach

Nico’s parents, Lorena and Juan, said in a statement they were “heartbroken” to share the news.

“We are heartbroken to share that our son, Nico, has passed away,” the family said.

“Nico was a happy, friendly, and sporty young boy with the most kind and generous spirit.

“He was always full of life and that’s how we’ll remember him.

“We would like to sincerely thank the first responders and the teams at Sydney Children’s Hospital, Randwick for everything they did to care for Nico.

“We would also like to thank everyone in the community for their support and kind messages.

“We ask you please respect our privacy during this exceptionally difficult time.”

String of shark attacks

Nico, a junior lifesaver, was the first of four shark attack victims in 48 hours on NSW beaches this week after a weekend of wild weather.

A surfer, 27-year-old musician Andre De Ruyter, was attacked in the water at a Manly beach on Monday.

He was pulled to shore by fellow surfers and remains in a critical condition, with part of his lower right leg amputated.

Hours early at nearby Dee Why Beach on the northern beaches an 11-year-old surfer had his board bitten by a shark.

The whole stretch of beaches were closed.

The next day a man was attacked at Point Plomer, north of Port Macquarie.

He only suffered minor injuries and has since been discharged from hospital.

This morning a shark sighting at Manly forced the closure of the beach just hours after flags were set up for the day.

The state’s recent wet weather, considered a once-in-a-500 year event, has been a perfect storm for bull sharks to lurk in coastal waters around Sydney and the rest of NSW.

Heavy rain means more fresh water than usual is running through rivers and estuaries into saltwater systems and beaches, creating brackish water.

This is a phenomenon where fresh and saltwater mix, being saltier than normal freshwater, but less salty than typical seawater.

“Bull sharks are also one of the few species of sharks and rays that can tolerate brackish and even freshwater for extended periods,” Professor Jodie Rummer from James Cook University said.

“Which means they are especially comfortable moving in and out of river mouths and turbid coastal waters after heavy rain.”