An elderly woman was out walking her 15-year-old dog Daisy when the pair were attacked by an American Staffordshire terrier.

The Staffy ran out of a gate that had been left open and in Penrith, Sydney, mauling Daisy to death and knocked the 87-year-old woman to the ground.

A neighbour who was driving past saw the woman on the ground and quickly pulled over to help, according to 9NEWS.

Paramedics help an 87-year-old woman to an ambulance after a large Staffy knocked her down

The woman's 15-year-old dog Daisy was killed by the loose American Staffordshire terrier

The Staffy's owner arrived on the scene within seconds, but was unfortunately too late to save Daisy,

Penrith City Council released a statement saying that the dog had been placed it in Hawkesbury Animal Shelter after it was surrendered by its owner.

An application for the animal to be euthanised is currently being formalised by the council.