The city has issued its first extreme cold weather alert of the season as Toronto braces for a blast of wintry weather.

Temperatures are expected to plunge as low as –15 C overnight — the threshold for such alerts — and will rise no higher than –11 on Monday according to Environment Canada.

Residents are encouraged to dress in warm layers and to call or visit friends, neighbours and family who might be having trouble with the cold weather. Infants and young children, the homeless, people who work outdoors and those with heart or respiratory illnesses are among those at risk, officials say.

The alert triggers additional services for the homeless including the opening of two 24-hour drop-in centres, additional shelter beds and increased street outreach.

If you see someone on the street who needs help with the cold call 311 or, for medical emergencies, 911.

Dr. David McKeown, the city's medical officer of health, said the alert will be in effect until further notice.