Temperatures are expected to take a dramatic plunge after a mild and sunny day on Tuesday, prompting Toronto Public Health to issue an extreme cold weather alert.

Environment Canada is predicting a high of 12 C on Tuesday afternoon, with clouds moving in during the evening and a temperature drop to -12 C and a wind chill of -21 C. There's also a small chance of flurries overnight.

"Even though today's nice, you need to seek shelter overnight, and if you live at home, make sure your heat is still on — especially if you have infants or older people living with you," said Dr. Christine Navarro, Associate Medical Officer of Health with Toronto Public Health.

Cold weather alerts activate city services that focus on increasing the amount of space in shelters and drop-in centres to keep vulnerable people inside.

Navarro advises anyone who is seeking shelter to call 311 to be directed to the closest location.

There have been 22 cold weather alerts issued in the 2016 to 2017 winter season.