A police officer secures the scene in Montreal where Nick Rizzuto, the son of Vito Rizzuto, so-called head of Canada's Mafia, was apparently shot and killed. (Graham Hughes/Canadian Press)

The son of Canada's most powerful mobster has been gunned down in Montreal's 31st homicide of the year, according to a report from the French-language service of the CBC.

The Radio-Canada report says Nick Rizzuto Jr., the 42-year-old son of alleged Montreal mob boss Vito Rizzuto, was shot Monday afternoon in the city's Notre-Dame-de-Grâce district.

The report describes a gangland-style killing near the corner of Upper Lachine Road and Wilson Avenue, one of the grittier parts of Notre-Dame-de-Grâce.

A man was standing on a busy street near a black Mercedes sedan when at least one gunman approached and fired several shots, the report said. Witnesses said the man crumpled into the fresh snow and police soon arrived to take him to hospital.

The gunman fled the scene, investigators said.

Police haven't confirmed the victim is Nick Rizzuto and are still interviewing witnesses. Montreal police spokesperson Const. Olivier Lapointe said a few witnesses gave partial descriptions of the gunman but did not have precise details.

Vito Rizzuto is in a medium-security prison in Colorado, serving a 10-year sentence for racketeering, relating to three murders in Brooklyn in 1981. Nick Rizzuto Jr., who was named after his grandfather, has never been charged with a criminal offence, according to the Montreal Gazette.

Michel Auger, an expert on organized crime in Montreal, said the last time a high-ranking member of the Montreal mafia was gunned down was in the 1970s.

Crime experts predict reprisals

Another expert on the Italian Mafia said the killing could spark an escalation in gangland violence.

"This is an unprecedented challenge to the Rizzuto crime family," said Antonio Nicaso, the author of several books on the Mafia. "Since [the 1970s] they were in charge of criminal activity in Montreal — without any challenge to their authority."

"There will be, for sure, a retaliation," Nicaso said. "The son — the eldest son — of Vito Rizzuto was killed. This is not just an ordinary member of the family."

Nicaso says the killing may be related to a string of recent firebombings of Italian coffee shops in Montreal, and could have been the work of street gangs.

With files from The Canadian Press