The alert opens two 24-hour emergency shelters in the downtown core, and makes more outreach and transportation services available to the city's homeless.
The city has been under pressure to do more for the city's homeless after two men died during a cold snap earlier this month.
The temperature is expected to drop to -16 C tonight, one degree below the traditional threshold for extreme cold weather alerts.
If you see someone on the street who needs assistance such as a shelter bed, call 311. For medical emergencies, call 911.
The alert remains in effect until further notice.