The son of mobster Vito Rizzuto -- sometimes called the head of Canada's mafia -- has been gunned down in a brazen daylight shooting in Montreal.

Nick Rizzuto, 42, died in front of several witnesses in Montreal's Notre-Dame-de-Grace district.

A lone gunman approached the victim as he stood near a black Mercedes sedan. Police said Nick Rizzuto was shot and killed at close range.

Police rushed to the scene and took the victim to hospital, where he was pronounced dead.

CTV Montreal's Paul Karwatsky said despite there being a number of witnesses, no one has come forward with a description of the gunman.

"(There were) a lot of people on this street, a lot of witnesses to this crime," he told CTV News Channel Monday evening.

He said witnesses described four quick shots, a pause, followed by another two shots.

Experts fear that the murder could be the start or the escalation of a gang war in Montreal. Already more than a dozen businesses have been firebombed in recent months.

"This is an unprecedented challenge to the Rizzuto crime family. . . Since (the 1970s) they were in charge of criminal activity in Montreal -- without any challenge to their authority," Antonio Nicaso, an expert on Canadian crime, told The Canadian Press.

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

Montreal has now had 31 homicides this year.

Vito Rizzuto is serving a 10-year prison term in Colorado for racketeering. The conviction is linked to three murders carried out in Brooklyn in 1981.

With files from The Canadian Press