MONTREAL -- As the coldest night of the year, so far, descends on Montreal, the city has urged citizens to keep a watchful eye on vulnerable populations.

Call 211 to find community and social resources, 911 if there's an emergency.

As the temperature dips to -20, and winds make it feel even colder, Montreal's estimated 3,000 homeless are at risk, Mayor Valerie Plante warned on Thursday.

Montrealers shouldn't hesitate to call emergency services, she said.

The city and its partners have more than 1,100 spots available at shelters, including at the old Royal Victoria Hospital--where pets are accepted.

There are also two warming centres: one on President Kennedy St. with 55 spots and another on Ontario St. where those who don't fit into the traditional shelter system can warm up overnight.

With files from CTV Montreal's Annie Demelt