More than 1,000 flights were canceled and hundreds more delayed in the US on Monday after a winter storm blasted much of the country with heavy snow and ice.

A total of 1,339 flights were canceled and 606 flights were delayed, as of 6:45 a.m. ET, according to flight-tracking website FlightAware.

Southwest Airlines canceled 265 flights, the most among airlines, followed by American Airlines with 176. Reagan National Airport in Washington, DC, canceled 234 flights, the most among airports and making up 58 % of all scheduled flights there, based on data.

Major US airlines issued travel advisories between Saturday and Monday, including Delta, American, United Airlines and Southwest.

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As the storm moved into the mid-Atlantic region on Monday, more than a dozen states from Kansas and Missouri to New Jersey were under winter storm warnings and advisories.

Southwest Airlines canceled 265 flights Monday, the most among the airlines. (Kevin Dietsch/Getty Images, File/Getty Images)

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“For locations in this region receiving the highest snow totals, this may be the heaviest snowfall in at least a decade,” the National Weather Service said.

A vehicle travels west in blizzard conditions during a winter storm on Interstate 70 in Topeka, Kansas, on January 5, 2025. (Evert Nelson/The Capital-Journal/USA Today Network via REUTERS/Reuters Photos)

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Washington DC Mayor Muriel Bowser declared a snow emergency until at least the end of the day Tuesday, while Maryland Gov. Wes Moore declared a state of emergency and warned residents to avoid travel.

Reuters contributed to this report.