Sgt. Laurent Gingras, a spokesman for the Montreal police, said all the incidents happened between 8 p.m. and 8 a.m.
Alleged victims and witnesses reported seeing the handle of a gun or having a gun shown to them.
"In LaSalle, or anywhere else on the island, if you're carrying a cell phone with you just be aware of your surroundings," Gingras said.
Police are warning people that if they are the victim of a mugging, they should not try to argue with the aggressor or fight back. They should do as they are told and then report the incident to police.
Gingras said anyone with a mobile device should get the International Mobile Equipment Identity (IMEI) number by dialing *#06#.
"That gives you a unique number that's associated with your phone. If you get robbed or lose your phone, you give your provider that number and your phone is deactivated. You can also give that number to police and they put it on a blacklist, which we hope makes the phone unusable to the person who robs it. "
The police investigation into the recent string of thefts is ongoing.