TORONTO -- The city’s medical officer of health has issued an extreme cold weather alert ahead of a massive temperature drop overnight.

Toronto will see a high of -5 C today but the temperature is expected to steadily drop until it hits around -17 C at around 7 a.m. on Saturday. Environment Canada says it will feel closer to -25 with the wind chill.

Extreme cold weather alerts are usually issued when the daily forecast suggests temperatures will reach approximately -15 C or colder, or when the wind chill is forecast to reach -20 or colder.

In addition to year-round 24-hour respite sites already open across Toronto, a warming centre will be open at Metro Hall starting tonight at 7 p.m. It will remain open until noon on the day the alert ends.

The city also offers enhanced overnight street outreach and transit tokens at some drop-ins while the alert is in effect.

Public health officials are urging members of the public to check on vulnerable family members, friends, and neighbours during the frigid weather.

Those at the greatest risk of cold-related illnesses are people experiencing homelessness, those who work outdoors, elderly people, infants, and those with pre-existing heart of respiratory conditions.

The temperature is expected to warm up slightly on Saturday afternoon.

Environment Canada says Toronto will see a high of -8 C and it will feel closer to -11 in the afternoon.

Warmer weather arrives on Sunday and will continue into next week.