Mosman couple Genna Merrin and George Toussaint, who were at Rose Bay wharf when the boy arrived aboard the police boat, said the officers treating the 12-year-old were “covered in blood”.

The boy remains in an induced coma in Sydney Children’s Hospital at Randwick, where he underwent surgery on Sunday.

“That boy is fighting for his life now,” McNulty said.

“He’s surrounded by his family and friends … and our thoughts and prayers go to him and his family right now.”

NSW Ambulance Inspector Giles Buchanan said the actions of the officers aboard the Water Police 41 were “definitely a life-saving intervention”. By the time the boy reached Rose Bay ferry wharf, he had to be resuscitated, Buchanan said.

The boy received several blood transfusions before arriving at hospital.

“It was touch and go the entire time,” Buchanan said.

McNulty praised the bravery of the boy’s friends, who on Sunday night were assisting detectives.

“The actions of his mates who have gone into the water to pull him out have been nothing but brave,” he said.

“Those young men are brave under those circumstances, and very confronting injuries for those boys to see. But I suppose that’s mateship.”

The species of shark involved in the attack is yet to be formally identified, but, based on the bite marks on the boys legs, is believed to be a large bull shark.

McNulty said a combination of “brackish” water in the harbour caused by heavy rainfall across Sydney over the weekend and the splashing of the boy and his friends had created a “perfect storm environment for that shark attack”.

“We’ve experienced a lot of fresh water in the harbour,” he said.

“You can’t see the bottom of it, it’s brackish water, so I would recommend not swimming in the harbour or other river systems across NSW at this time.”

Bull shark activity peaks in Sydney Harbour between January and February. Large females swim up estuaries and give birth to their young in waterways including the Hawkesbury and Parramatta rivers. Bull sharks are aggressive, territorial, and prefer brackish water.

Sunday’s attack came almost two years after kayaker Lauren O’Neill survived a bull shark attack at Elizabeth Bay.

Mercury Psillakis, 57, died after he was bitten by a shark while surfing at Long Reef Beach on Sydney’s northern beaches in September. Surfers had reported seeing a six-metre white shark in the area.

Swiss tourist Livia Mühlheim, 25, was killed in a shark attack while swimming with her partner, Lukas Schindler, at a remote beach on the NSW Mid North Coast in November. Authorities believe a mature bull shark at least three metres long attacked the couple.