An SPCA spokesperson said the cat's injuries were "shocking" and "one of the worst injuries like this our Christchurch team have ever seen".
The spokesperson said when the cat was brought into the centre her leg was hanging off.
"Vets had to perform an emergency amputation, and fortunately the cat is now recovering well."
She is a three-year-old tabby and was found in the Riccarton area.
"We have no idea how she sustained such a terrible injury," the spokesperson said.
"We believe she has an owner as she was wearing a collar, but sadly wasn’t microchipped. We are about to post on our Facebook page to see if we can find them."