An arctic cold snap has sent temperatures plunging across the Midwest , prompting officials to close schools, business and state government offices across the region.

The U.S. Postal Service took the rare step of suspending mail delivery across much of the region. More than 1,600 flights were canceled at Chicago’s airports Wednesday, including more than 1,300 at O’Hare International Airport, one of the nation’s largest airports.

The bitter cold is the result of a split in the polar vortex that allowed temperatures to drop much farther south than normal. That meant temperatures in parts of the Midwest were lower Wednesday than in parts of Antarctica.

Officials in several cities are focused on protecting vulnerable people from the cold , including the homeless and those living in substandard housing. Some buses were turned into mobile warming shelters in Chicago.

Ice forms along the shore of Lake Michigan before sunrise, Wednesday, Jan. 30, 2019, in Chicago. A deadly arctic deep freeze enveloped the Midwest with record-breaking temperatures on Wednesday, triggering widespread closures of schools and businesses, and prompting the U. (AP Photo/Kiichiro Sato)
Ice forms along the shore of Lake Michigan before sunrise, Wednesday, Jan. 30, 2019, in Chicago. A deadly arctic deep freeze enveloped the Midwest with record-breaking temperatures on Wednesday, triggering widespread closures of schools and businesses, and prompting the U. (AP Photo/Kiichiro Sato)
A person walks along the lakeshore, Wednesday, Jan. 30, 2019, in Chicago. A deadly arctic deep freeze enveloped the Midwest with record-breaking temperatures on Wednesday, triggering widespread closures of schools and businesses, and prompting the U. (AP Photo/Kiichiro Sato)
A person walks along the lakeshore, Wednesday, Jan. 30, 2019, in Chicago. A deadly arctic deep freeze enveloped the Midwest with record-breaking temperatures on Wednesday, triggering widespread closures of schools and businesses, and prompting the U. (AP Photo/Kiichiro Sato)
Geese huddle in the water as the sun rises at the harbor in Port Washington, Wis., on Wednesday, Jan. (AP Photo/Jeffrey Phelps)
Geese huddle in the water as the sun rises at the harbor in Port Washington, Wis., on Wednesday, Jan. (AP Photo/Jeffrey Phelps)
Icicles form on a railing as the sun rises in the harbor in Port Washington, Wis., on Wednesday, Jan. (AP Photo/Jeffrey Phelps)
Icicles form on a railing as the sun rises in the harbor in Port Washington, Wis., on Wednesday, Jan. (AP Photo/Jeffrey Phelps)
Ice covers the Chicago River Wednesday, Jan. 30, 2019, in Chicago. A deadly arctic deep freeze enveloped the Midwest with record-breaking temperatures triggering widespread closures of schools and businesses. (AP Photo/Teresa Crawford)
Ice covers the Chicago River Wednesday, Jan. 30, 2019, in Chicago. A deadly arctic deep freeze enveloped the Midwest with record-breaking temperatures triggering widespread closures of schools and businesses. (AP Photo/Teresa Crawford)
Lisa Laws is bundled up as she has a CTA bus to herself early Wednesday, Jan. 30, 2019.  The cold struck Chicago transportation Wednesday morning, with more than 1,600 canceled flights and limited rail service.  (Rich Hein/Chicago Sun-Times via AP)
Lisa Laws is bundled up as she has a CTA bus to herself early Wednesday, Jan. 30, 2019. The cold struck Chicago transportation Wednesday morning, with more than 1,600 canceled flights and limited rail service. (Rich Hein/Chicago Sun-Times via AP)
A bundled-up commuter makes their way through the loop early Wednesday, Jan. 30, 2019 in Chicago. A deadly arctic deep freeze enveloped the Midwest with record-breaking temperatures triggering widespread closures of schools and businesses.  (Rich Hein/Chicago Sun-Times via AP)
A bundled-up commuter makes their way through the loop early Wednesday, Jan. 30, 2019 in Chicago. A deadly arctic deep freeze enveloped the Midwest with record-breaking temperatures triggering widespread closures of schools and businesses. (Rich Hein/Chicago Sun-Times via AP)
A commuter braves the wind and snow in frigid weather, Wednesday, Jan. 30, 2019, in Cincinnati. The extreme cold and record-breaking temperatures are crawling into a swath of states spanning from North Dakota to Missouri and into Ohio after a powerful snowstorm pounded the region earlier this week. (AP Photo/John Minchillo)
A commuter braves the wind and snow in frigid weather, Wednesday, Jan. 30, 2019, in Cincinnati. The extreme cold and record-breaking temperatures are crawling into a swath of states spanning from North Dakota to Missouri and into Ohio after a powerful snowstorm pounded the region earlier this week. (AP Photo/John Minchillo)
 Drivers navigate their way through downtown St. Joseph, Mich., Wednesday, Jan. 30, 2019, in subzero temperatures and near whiteout conditions.(Don Campbell/The Herald-Palladium via AP)
Drivers navigate their way through downtown St. Joseph, Mich., Wednesday, Jan. 30, 2019, in subzero temperatures and near whiteout conditions.(Don Campbell/The Herald-Palladium via AP)
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