MINNEAPOLIS (AP) -- Schools, businesses and government offices remained closed with dangerously cold temperatures stuck well below zero in Minnesota.

Minneapolis, St. Paul, Anoka-Hennepin, Rosemount-Apple Valley-Eagan, Robbinsdale and Duluth schools canceled classes again Thursday. The National Weather Service issued a wind chill warning until noon. Temperatures will be cold enough to produce wind chill readings of negative 55 in Minnesota and elsewhere in the region.

The extreme cold has sent dozens of people to hospitals in Minnesota. Hennepin Healthcare in Minneapolis has treated 22 patients for frostbite since Friday, including 13 admitted to the hospital. The hospital also has treated numerous other people for cold-related injuries.