The schoolgirl was walking hand-in-hand with her mother in Golders Green Crescent at 6pm on Saturday.
The family passed two women with a blue nose pitbull on a lead when “out of nowhere” it grabbed the girl in its jaws and pulled her to the floor.
She was savagely bitten five times by the dog and suffered serious injuries to her arm as she tried to defend herself.
Her mother told the Standard: “I didn’t know what to do. It all happened so quickly and the dog was so powerful. I have never seen anything like it before.
“My daughter put her arms in front of her face because the dog was aiming at her neck.
“The lady could not pull the dog off.
“I kicked the dog and managed to pull her out from under the dog before a man managed to hold the dog down.
“I was in absolute shock and so was my daughter.
The mother said it took 30 minutes for the ambulance to arrive and by that time “someone had hidden the dog away”, she claimed.
She hailed the “amazing hospital staff” and said after two nights and an operation her daughter was able to return home on Monday.
She added: “She is much better and is recovering. She is in trauma and shock and is very afraid of dogs. I told her it’s not the dogs it’s the owner’s lack of training. It will take her a bit of time.
“If my daughter didn’t cover her face then she wouldn’t be alive right now.
“She still moans in pain from the injuries and doctors have said it will take a very long time for the wounds to heal.”
Scotland Yard has been approached for comment.