Canada's ruling Liberal Party lost a once-safe seat in a Montreal parliamentary constituency, preliminary results showed on Tuesday, a result likely to put more pressure on Prime Minister Justin Trudeau to quit.

The loss, coupled with a recent Toronto defeat, signals waning support for Trudeau, who faces a challenging re-election campaign.

Prime Minister Justin Trudeau has been handed his second byelection upset in recent months, as the Bloc Quebecois has just won LaSalle-Emard-Verdun, Que., a longtime Liberal seat in Montreal.