Staff from Taronga Zoo, the National Parks and Wildlife Service and the Organisation for the Rescue and Research of Cetaceans (ORCCA) were called to the scene and provided the seal with medical care.

Mark Williams, of Taronga Zoo, said the seal was probably caught in a current, which took her thousands of kilometres north from her Antarctic home, to the beaches of Sydney.

``By the time she made it to Kurnell, she was is a terrible condition,'' Mr Williams said.

``She was suffering from shark bites and was very emaciated.''

Mr Williams said the situation was a ``medical emergency''.

The seal was found by Simone Picken of Cronulla, who was walking her dog along the beach.

``It looked very malnourished. You could see its skeleton pressed against its skin,'' Ms Picken said.

The seal is now being treated at Taronga Zoo, where veterinarians said it was ``difficult to predict whether she will survive or not''.

A leopard seal that washed up on Wattamolla beach in the Royal National Park in a similar condition last September made a full recovery.

``Casey'', as he became known to veterinarians at Taronga Zoo, weighed 90-kilograms and was ``at death's door'' when he was found.

On recovery, he weighed a healthy 200-kilograms.

A National Parks and Wildlife Service spokeswoman said now was the time of year when seals were seen on Sydney beaches.

``They are not always injured and sick like this one. Sometimes they are just there to sunbathe,'' she said. ``We warn residents never to get close, as seals can be dangerous because of their big teeth.''

The Leader was contacted by residents who saw an Australian fur seal frolicking near Captain Cook's landing place at Kurnell on Sunday.

The spokeswoman said residents who found a seal on a southern Sydney beach should call the Kurnell office of National Parks and Wildlife Service on 96682000.