Nearly 750 flights at Denver International Airport have been canceled as of Wednesday afternoon as severe weather threatens to bring blizzards to the central U.S.

Major airlines including Southwest and United, among others, had canceled much of their Denver activity, with Southwest and United canceling just about half of its Wednesday flights — 201 and 181 cancellations, respectively. SkyWest canceled 155, or 53 percent, as of Wednesday afternoon, according to The Denver Post.

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More than 150 flights had already been canceled for Thursday as well, according to data from Flight Aware.

The National Weather Service's Weather Prediction Center said the storm system will move over the Rockies and into the Northern Plains by Wednesday night, bringing heavy and wet snow to the region.

South Dakota is expected to experience the heaviest snowfall, with travel predicted to be “difficult to impossible” based on wind and visibility.

As of early on Wednesday, blizzard warnings had been placed in effect in 6 states, stretching from Colorado all the way up to Minnesota, according to Fox News Senior Meteorologist Janice Dean.

Many of the major airlines, including Southwest, United, American and Delta, are providing travel waivers, or extending no-cost change fees amid the storms.

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Fox News’ Travis Fedschun contributed to this report.