A woman has suffered serious injuries to her leg in a shark attack in Sydney Harbour.
The 29-year-old was swimming at a private wharf at Billyard Avenue, Elizabeth Bay just before 8pm when she was bitten on her right leg.
It is believed she had just jumped off the wharf and was swimming out to a boat when she was attacked.
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Witnesses jumped in to save her and pulled her back to land, including a vet who applied a tourniquet to her leg to stop the bleeding until paramedics arrived.
“My wife’s a vet and she basically bandaged it up,” the woman’s wife told 7NEWS.
“The bone’s broken, it’s pretty hectic but she seems to be OK.
“She’s in a lot of shock, we kept her warm.”
Had the woman been further out in the water, “she wouldn’t have survived”, she added.
NSW Ambulance said the woman suffered critical injuries and severe blood loss from injuries to her lower leg.
A rescue helicopter was on standby, but she was taken to St Vincent’s Hospital by road and was in a serious condition as of Tuesday morning.
7NEWS understands she will undergo surgery later on Tuesday.
Witnesses believe it was a bull shark, which are common in the harbour, but the species has not been confirmed.
“Police have been told she was swimming off the wharf at the time,” NSW Police said.
“Marine Area Command are patrolling the area as a precaution.”