St-Colomban issued a state of emergency for a maximum of 48 hours after 60 millimetres of rain caused waterways to overflow, washing out roads and flooding homes and farmland.
St-Colomban Mayor Jean Dumais said at least dozens of people are trapped in their homes and that the water level is rising inside houses and in the streets.
The flooding was so forceful in St-Colomban that the land running alongside major roads has eroded to a point where massive crevices have opened up.
At least one resident's driveway has cracked so wide that a culvert that normally runs under the asphalt is now exposed and has water rushing through it.
Rivière-du-Nord Road to the east and west of St-Colomban is closed.
Flooding in Montreal, western Quebec
In Gatineau and on the island of Montreal, minor flooding filled underpasses, rushed parking lots and washed out yards of homes.
CBC Ottawa-Gatineau reported that a number of cars had been heavily damaged by flooding.
In Montreal, underpasses at Salaberry in Cartierville and Atwater in St-Henri filled with water overnight. However, most of the roads cleared by Wednesday morning.
In Île-Bizard, on the West Island, emergency crews responded to six homes on Roy and Paquin streets where water had entered their basements.
Laval, St-Eustache, Ste-Thérèse and Oka were also affected by flooding.