Jackline Anchito and her daughter were with several women leaving the Melbourne home Wednesday when the dog attacked, the Australian Broadcasting Corp. reported.
They ran back into the house but the dog followed them, attacking the 4-year-old and severely mauling her.
The girl died at the scene despite efforts by emergency medical personnel to save her, officials said.
The dog, believed to have escaped from a neighbor's yard, will be destroyed, but it has not been decided if the owner will face charges, police said.
"This is a really horrible tragedy, and it will take some time for us to fully understand what has happened," police Superintendent Graham Kent said.