Police in Calgary have a man in custody following a slashing attack on an 11-month-old infant early Saturday morning.

Police discovered the injured baby after receiving a 911 call from a man inside a house in the 1000 block of Cranston Drive SE at about 4 a.m. MT.

Roxie O'Brien, a neighbour, said she was already awake when she heard noises coming from her neighbours' open window.

"I heard a guy yelling and then a baby crying," she said.

Stu White, who is visiting two doors away, was shaken by what he witnessed: "We saw them take the baby out on the stretcher," he said.

The infant boy, who was in critical condition when taken to Children's Hospital, has since been upgraded to stable.

Insp. Bruce Walker said police arrested an "agitated" man who allegedly slashed the infant several times.

Mother still missing

The Calgary Police Service's child abuse unit is investigating. Police are not certain that anyone else was in the home at the time of the incident, but believe others do live there.

They want to speak with those residents, as well as the infant's mother. Officers checked with neighbours, brought out tracking dogs and checked local hospitals, but have not found her.

Drew Thacyk, a neighbour, said a couple bought the house within the past two years and he's never had trouble with them.

"I think it's just crazy," he said. "I have a hard time believing it.

"[The father] was the proudest guy ever when he had that baby. He was so excited … and just a really nice guy. They both were really nice."