An extreme cold weather alert has been issued by the City of Toronto as temperatures are expected to dip to -20C with the wind chill on Saturday.

Officials prompted the warning as the forecast calls for an overnight low closer to -30C.

The alert causes city services to spring into action, opening up 80 additional emergency sleeping spaces for homeless people and providing enhanced street outreach services.

Emergency TTC tickets will also be issued through drop-in centres, allowing homeless people to get a free ride to shelters.

The public can also call a 24-hour toll-free number if they see a homeless person sleeping outside in the cold weather. The Street Helpline can be reached at 1-866-392-3777.

There have been several extreme cold weather alerts issued since winter finally moved in after a balmy start to the season.

Temperatures are expected to stay cold for the next several days.