A bull shark is suspected of carrying out the attack. Photo: 123RF / Oliver Petschner
A local vet has been praised for "absolutely" saving the life of a woman who sustained a serious leg injury in a shark attack in Sydney Harbour.
Lauren O'Neill was attacked near a private wharf near Billyard Avenue in Elizabeth Bay just before 8pm on Monday.
Emergency services, including paramedics and a rescue helicopter, responded to triple-0 calls from neighbours and she was treated at the scene for a serious injury to her right leg.
"She has been taken to St Vincent's Hospital in a stable condition," police said in a statement.
"Police have been told she was swimming off the wharf at the time.
"Marine Area Command are patrolling the area as a precaution."
Department of Primary Industries shark scientists have assessed O'Neill's injuries and determined a bull shark was likely responsible.
Michael Porter, who is her neighbour, said he heard a "soft yell for help" outside his window.
"I looked outside and saw [her] propped on the ladder, external to the harbour pool, trying to climb in, and behind her was her leg, which was limp and completely open, and a pool of dark red blood behind her," he said.
"Straight away, grabbed my phone, starting sprinting outside and called triple-0."
A bystander said O'Neill was "OK" but in a "lot of shock".
"She swam out to the boat and on the way back she got bitten by, I think it was a bull shark," she said.
"So we ran out - my wife's a vet - and she basically bandaged it up. The bone's broken and it's pretty hectic actually.
"We got some bandages, we kept her warm, and my wife basically bandaged her up, stopped the bleeding because if she got bitten out there [further from shore] she wouldn't have survived."
Porter said the vet "absolutely saved her life, in my opinion there is no question about it".
Shark attack survivor offers support
NSW Department of Primary Industries marine ecologist Amy Smoothey said the attack was "tragic" and not "common".
She said the department's research found that there were "numerous" bull sharks in coastal areas and waterways, such as Sydney Harbour, in the months of January and February due to warmer water temperatures.
Smoothey said authorities are unlikely to find the shark who bit O'Neill because they "don't stay in one particular location".
She urged swimmers to exercise caution when swimming in the water during the summer months but said the chances of another bull shark attack occurring was "incredibly low".
Shark attack survivor and former navy diver Paul de Gelder said he hoped the woman was OK.
"My best wishes go out to the young lady that was bitten yesterday," he told the ABC.
"In the days to come of healing, if I can be of any help or support then I welcome her to reach out."
De Gelder sustained horrific injuries to one of his arms and legs when he was attacked by a bull shark during a counter-terrorism exercise in Sydney Harbour in 2009.
City of Sydney Councillor Linda Scott has cautioned people to stay out of the water in the harbour.
"I'm extremely concerned to learn of a shark attack in our City of Sydney," she wrote on Instagram.
"Please, stay out of the harbour until further notice.
"Thank you to the bystanders who stood in to bravely help and to St Vincent's Hospital Sydney for their care of the victim."
This story was first updated by the ABC.