The as yet unnamed baby was attacked by the family's pet dog at a house in Nelson, Lancashire on Wednesday morning.
Officers who rushed to the scene confirmed the tiny youngster was taken by air ambulance to the Royal Blackburn Hospital before later being transferred to the Royal Manchester Children's Hospital.
Police confirmed the small child is currently stable and her wounds are described as "serious cuts".
Upset neighbours described the shocking incident, with a female resident saying she saw emergency services arrive.
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The American Bulldog is a legal breed in the UK and a powerful working dog.
The little girl was attacked by her pet Bully, a type of American Bulldog named after influential breeder John D. Johnson.
Banned dogs in the UK are the Pit Bull Terrier, the Japanese Tosa, the Dogo Argentino and the Fila Brasileiro.
An investigation has been launched into the incident but no arrests have been made.
A Lancashire Police spokesman said: "We were called shortly after 11.30am on Wednesday to a report that a child had been bitten by a dog.
"Her condition was described as serious but now she is stable.
"An investigation into the circumstances is under way and at the moment there's nothing to suggest any criminal offices have taken place.
"The girl has not suffered any major injuries, just cuts which were serious but not life-threatening," the police spokesman added.