Mary Gallagher was walking Maxwell, a Yorkshire terrier, in Sydney Road, Muswell Hill, on Sunday when the aggressive mutt lunged towards him.
The 11-year-old dog died instantly but the pit-bull refused to let go as he chewed through little Maxwell’s body.
He made grunting sounds and his mouth began dripping with blood as he continued to decapitated the pet, while a hysterical Ms Gallagher watched on.
The 53-year-old said: “There was blood everywhere, all down the road, it was like a massacre. He had a firm grip on Maxwell’s stomach and wouldn’t let go.
“He then took Maxwell’s head into his mouth and began swinging it around. A man came out with a plank of wood and began whacking the pitbull round the head but he didn’t stop.
“He was so violent. I was in hysterics, screaming, shouting, looking for someone to help me.
“I tried kicking the dog but he kept resisting, I fell into the bushes while jumped up and down with the dog in his mouth.”
When the mutt finally let go of Maxwell, his owner appeared and cautioned Ms Gallagher to stay away because of his history of violence.
When the police arrived, it emerged the pitbull was supposed to be muzzled and kept on a lead when he is out in public.
Detectives seized the dog and it will likely be put down.
The dog belonged to Ms Gallgaher’s daughter, Laura, who lives in Colney Hatch Lane, Muswell Hill.
The pair have been unable to sleep or eat and are constantly faced with haunting flashbacks about the attack.
Moments after it happened, Laura, 21, a dental nurse who works in North Finchley ran outside in her pyjamas after hearing something had happened to her dog.
She said: “I screamed and a woman pointed to where my dog was but everyone was holding me back saying don’t look. A guy put a sheet over him.
“I broke free from their grip and screamed – and ran over to my dog. I saw he was dead, his guts were hanging out and his tongue was out, his eyes were open.
I collapsed to the floor. The dog still had blood dripping from his mouth and it made me angry. I began punching the wall and fence, screaming.
“Another dog walked past with its owner and it began grunting, it looked like it was ready to kill again.”
Laura had formed a special bond with her pet when she got him as a present at the age of ten.
She added: “He was lovely and friendly, always played with other dogs and was very gentle. He loved playing with his toys.
“He would never leave our side. Even when we went to the park and let him off his leash, he’d always stay close to us.
“We are going to miss him so much. Nothing will bring him back. We’ve buried him in our back garden and I’m out there all the time now, I want to be close to him.”
In a statement, police said: “We were called to Sydney Road to reports of a dog fight. On arrival officers found a Yorkshire terrier dog that had allegedly been attacked by another dog.
“The Yorkshire terrier was dead when police arrived.
“The attacking dog was seized following and has been referred to the Met’s Status Dogs Unit.
“The animal is subject to registration conditions and is required to be muzzled, on a lead and kept in a secure environment.”