With more extreme cold weather in the forecast, the London-Middlesex Health Unit is issuing its fourth cold weather alert of 2015.
The Elgin-St. Thomas Health Unit has also issued a cold weather alert for that region.
Temperatures are forecasted to be below -15 C for the better part of the weekend, with temperatures dropping close to -20 C each night.
The alert comes into effect this evening and will continue until Tuesday, February 3. The daytime high on Tuesday is expected to reach -8 C.
Londoners are being asked to bundle up when heading outdoors and ensure there is little or no skin exposed to the cold.
Frostbite and hypothermia can occur within minutes of being outside in extreme cold.