More than 13,000 US flights were canceled from Saturday through Monday, as an "unusually expansive" winter storm descended across much of the eastern half of the country. 

More flights within, into or out of the US are scheduled to be canceled on Sunday, with disruption approaching levels not seen since the coronavirus epidemic, aviation analytics firm Cirium said.

Heavy snowfall, sleet and freezing rain threatened nearly 180 million people between the Rocky Mountains and New England, the National Weather Service (NWS) said on Saturday night. That's more than half of the entire populationof the US.

"The snow and the ice will be very, very slow to melt and won't be going away anytime soon, and that's going to hinder any recovery efforts," said Allison Santorelli, a meteorologist at the National Weather Service.

"By the time this event winds down late Monday, it will leave a trail of more than 2,000 miles of wintry precipitation, in a nearly continuous path, from New Mexico to Maine," the National Weather Service said.

US President Donald Trump also approved emergency declarations for multiple states to receive assistance from the Federal Emergency Management Agency.  

Here's what you need to know about the flight cancellations:

• All Saturday and Sunday morning flights were canceled at Will Rogers International Airport in Oklahoma City
• 700 departing flights and half of arriving flights were canceled at Dallas-Fort Worth International Airport
• Flights disrupted at airports in Chicago, Atlanta, Nashville and Charlotte, North Carolina
• All departing flights Sunday canceled at Ronald Reagan Washington National Airport
• Over 4,000 flights canceled across US on Saturday
• Over 9,000 flights canceled across US on Sunday 

More than 670,000 homes without power

The major storm has left thousands of families in the dark while forecasters warned that damage could rival that of a hurricane, especially in areas pounded by ice.

More than 670,000 households have been hit by outages nationwide, with more than 100,000 each in Texas, Mississippi, Louisiana and Tennessee, according to the website poweroutage.us on Sunday. 

Other states affected included Kentucky, Georgia, Virginia and New Mexico.

Storm of the decade

Georgia's senior state meteorologist warned people that this could be "perhaps the biggest ice storm we have expected in more than a decade."

"Ice is a whole different ballgame than snow," Lanxton said. "Ice, you can't do anything with. You can't drive on it. It's much more likely to bring down power lines and trees."

Georgia Governor Brian Kemp said he was deploying 120 National Guard members to the state's northeast, after having earlier put 500 of them on standby.

Houston Mayor John Whitmore urged residents to hunker down by late Saturday. "We're not used to what's supposed to be coming," he said.

New York City Mayor Zohran Mamdani urged New Yorkers to stay home if they could help it.

"Please, if you can avoid it, do not drive, do not travel, do not do anything that can potentially place you or your loved ones in danger," he said.

"Instead, I urge every New Yorker who can to put a warm sweater on, turn on the TV, watch 'Mission Impossible' for the 10th time, above all to stay inside."

Edited by: Roshni Majumdar