The neighbour had met the baby earlier in the day when the rottweiler escaped from the property and being familiar with the dog she helped put him back in the fence.
The mother was delighted about the baby being born the night before and had proudly shown the tiny baby to her, according to Stuff.
But she only returned later that evening when she saw a commotion down the street and she thought the dog must have escaped again.
It wasn't until she got closer that she was the mother was sitting on the grass holding the baby who was crying loudly.
"He was just so little," Karen, who then went and put her arms around the mother to comfort her, told Stuff.
"He was all dirty and had bits of blood on him.
"She told me which dog did it – they have two. It was the rottweiler."
It appeared that the woman had gone to the toilet when the rottweiler, about 2-years-old, attacked the baby and then tried to bury him.
"All she did was pop to the toilet and it happened just like that.
"The whole thing is horrible, every time I close my eyes I just see him."
Karen said she tied the dog up again that evening before animal control arrived as no one else was prepared to go near the dogs.
She said she almost felt guilty for returning the rottweiler earlier in the day given the tragedy that had unfolded later that night.
The Herald understands there were two dogs at the properly and one was not registered with the council.
Hamilton City Council confirmed animal control staff had collected a dog and was holding it at the council's animal control facility until the police investigation was completed.
In a statement, Hamilton City Council Animal Control Manager Susan Stanford staff were contacted by police shortly after 7pm on Sunday to attend a reported dog attack involving a baby in the suburb of Enderley.
The council declined to comment about the breed of the dog or whether it was registered - referring all questions to NZ Police.
The baby's death has been referred to the coroner.
