The mass slaying occurred at about 3:50 a.m. inside 1398 Alexander Ave., in the Weston neighbourhood, across the street from Weston School and just east of Quelch Street.
It was Winnipeg's first triple slaying since 1996 and instantly raised the city's homicide total to nine for 2008.
The names and ages of two males and one female gunned down inside the newer, two-storey home haven't been released. Three other victims -- two males and a female -- are in hospital with gunshot wounds.
City police said they had no idea what the motive was, and weren't aware of any violence at the address before, spokeswoman Const. Jacquie Chaput said at the scene.
Police had the whole area cordoned off throughout the day as they combed the neighbourhood for evidence and tried to protect the crime scene.
Several witnesses were being questioned by the major crimes and homicide units, Chaput said.
"It's a very rare occurrence... it's very disconcerting to us," she said. "In my recollection, there hasn't been a triple homicide since the incident on Semple (in 1996).
"We have a number of units and officers investigating this right now."
In 1996, three men were shot, execution-style, in a Semple Avenue home in West Kildonan.
The slayings were part of an ongoing battle between members of the Manitoba Warriors and associates of the Hells Angels over control of the drug and prostitution trades.
Two men were convicted of first-degree murder in the case and sentenced to life in prison, with no chance of parole for 25 years. A third accused was acquitted by a jury.
On Saturday morning, surprised neighbours said they had no idea the worst incident of violence in Manitoba in a dozen years was taking place so close.
"I didn't hear a thing," said one woman, who has lived on Alexander Avenue for more than 40 years. "I was awake when it would've happened."
The neighbourhood didn't seem any different than on any other night, she said.
She and other neighbours said they weren't aware of any commotion at the home.
She said her grown children are worried about her due to the triple slaying. "They're always asking me, 'When are you going to up and sell the house?' "
She was considering putting her house on the market this spring, and Saturday's shooting has helped her make up her mind.
Recently, there had been warning signs a major violent incident could be brewing, including three drive-by shootings in the past week. A justice source told the Free Press on Saturday that hostilities within the city's gang subculture have been escalating.
Members of two major gangs -- the Mad Cowz and Indian Posse -- were believed to be the most "active."
"There's no doubt they hate each other and there's been talk for awhile of things happening," the source said.
One of the major reasons for friction is control of the city's lucrative drug trade, which is very much an open market these days.
That's because the main supplier of drugs to the community, the Hells Angels, have been stung by two recent undercover operations that have resulted in most of their members and associates being locked up.
With the "big boys" out of the way, competition has heated up to fill the void. Gangs know selling drugs means quick, easy cash.
In the past week alone, there have been at least three reported drive-by shootings of houses in the inner city. Although no one was injured, sources say the incidents were a clear indicator of the growing gang hostilities.
The fact no arrests were many in any of the overnight attacks left open the possibility for more violence.
Other neighbours on Alexander Avenue expressed shock at the deadly incident.
"We just thought someone had been stabbed. We didn't hear any gunshots at all," said one woman, who didn't want her name published but lived close to the scene of the shootings.
She said a young family just moved into the newly built home about a year ago. She thought Habitat for Humanity or a similar organization had been involved in placement.
"There were two kids, a little girl maybe about nine, and a boy aged 10 to 12, and a mother. I didn't think anyone else lived there," she said.
"We didn't socialize with them, but it was very quiet there most of the time. I think sometimes on weekends the kids would go stay somewhere else and the mother would have friends over, but that's about it," she said.
Another nearby resident said he's been worried about violence in the home for months.
"I knew when they moved in there'd be trouble," he said, adding he's witnessed a constant flow of shady-looking people coming and going from the residence at all hours.
"My first question is just wondering what's happened to those kids. I hope they weren't home when this happened," he said.
"I've been telling my parents for the past year we have to get out of this neighbourhood."
Last month, an elderly man down the street from the shooting suffered life-threatening injuries after being stabbed in a home invasion. Three teens -- believed to be street gang members -- were arrested and are facing charges.