An elderly woman from Sydney's south-west has died after she was attacked by her pet dog on Thursday afternoon.

Rosemary O’Reilly, 72, from Wilton, suffered significant bite wounds and lacerations to her arms, legs and body when she was attacked by the large Staffordshire terrier-Rhodesian ridgeback cross at her home.

Rosemary O'Reilly and her husband owned the dog for about three years before it turned on them.

She was taken to Liverpool Hospital, but her condition deteriorated and she died while undergoing surgery.

A Wollondilly Shire Council spokesperson said the fatal attack was "extremely upsetting to us and our community".