Airlines in the United States canceled about 1,400 flights on Friday after a massive winter storm knocked out power and affected businesses in 12 states, with forecast for a brutal freeze over the weekend.
A total of 1,395 flights were canceled and 788 flights were delayed as of 8.16 am ET, according to flight-tracking website FlightAware.
"We expect some operational challenges due to the weather in the Midwest today and potentially tomorrow due to the winter weather in the region," Delta Air Lines said.
Southwest Airlines issued a travel advisory and said some of its flights in regions such as Chicago, Detroit and Omaha could be impacted.
The Federal Aviation Administration had on Thursday warned that clouds, snow and windforce could delay flights at certain airports.
Southwest led the list of cancellations with 270 flights followed by United Airlines Holdings at 252.
United also canceled some flights through Saturday as it awaits regulatory approvals to resume operating Boeing's 737 MAX 9 jets in the country.
The carrier said it was working to return its MAX 9 jets to service and was continuing to operate some planned flights by switching to other aircraft types.
The FAA had on Thursday launched a formal investigation on 737 MAX 9 after a cabin panel blew off an Alaska Airlines flight last week in mid-air, forcing an emergency landing.