A 13-year-old boy who is in intensive care following a shark attack in Sydney Harbour yesterday survived thanks to his friend jumping into the water to help him.

The boy, who is still fighting for life at Sydney Children’s Hospital, was jumping off a rock face at Vaucluse near Shark Beach when he was attacked by what police believe is a bull shark.

He sustained serious injuries to both of his legs, but was pulled from the water by emergency services, as well as his friends.

The quick thinking of emergency services and one of the boy’s friends helped save his life. (Nine)

“As soon as he was [in the water], he was bitten by a shark,” NSW Police Superintendent Joseph McNulty told Today.

“One of his mates jumped in and helped retrieve him from the water, and that’s some heroic actions just in itself.

“It was incredible bravery by that young man.”

McNulty later confirmed other friends helped pull the pair from the water onto a rockface.

“It was very confronting injuries for those boys to see, but I suppose that’s mateship,” he said.

Emergency services were called to Hermitage Foreshore Walk on Steele Point Road at Vaucluse at about 4.20pm.

The boy is still fighting for life at hospital. (Nine)

McNulty said a police boat arrived on scene, with responding officers offering immediate first aid, including a tourniquet system, and CPR.

“He applied that [tourniquet] to both limbs and stopped the [bleeding], which potentially saved that young boy’s life.”

The boy was taken to shore, where an ambulance crew was waiting.

Superintendent Joseph McNulty said the work of paramedics was “miraculous” to help save the boy’s life once he reached the shore. (Nine)

McNulty said paramedics performed a “miraculous” job to stabilise the boy, and praised the effort of police and paramedics to get him to hospital.

“They saved his life at that scene, we were losing his heart rate,” he said.

“We gave him a green light corridor all the way there. Thankfully, he’s still alive.”

NSW Ambulance’s Giles Buchanan said the boy had undergone surgery overnight, and outlined the efforts paramedics had to go to in order to save his life.

“By the time the patient was delivered to us, it was a resuscitation situation,” he said.

Paramedics had to revive the boy when he was taken ashore. (Nine)

“It required CPR, the medical team would have intubated the boy to take over his breathing for him.

“It was touch and go the entire time, and still he’s in a very dangerous position.”

McNulty said police suspect the boy was attacked by a bull shark due to the lacerations on his legs.

Marine biologist Lawrence Chlebeck said the recent rain in Sydney means bull sharks can be seen closer to the shore.

“They are the ones that can live in freshwater, they travel far up rivers, and after periods of rainfall, they come to these near shore areas,” he told Today.

Superintendent McNulty urged people to reconsider swimming in the harbour and rivers due to the recent heavy rain and the danger associated with it.

“It’s not a good time to swim,” he said.