Airlines in the United States canceled more than 1,600 flights on Friday after a massive winter storm knocked out power and affected businesses in 12 states ahead of a likely brutal freeze over the weekend.

A total of 1,643 flights were canceled and 1,238 flights were delayed as of 9.12 a.m. 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.</p> <p>Southwest Airlines said in a travel advisory that some of its flights in Chicago, Detroit and Omaha could be impacted.

The Federal Aviation Administration (FAA) had on Thursday warned that clouds, snow and windforce could delay flights at certain airports.

Southwest led the list of cancellations with 355 flights followed by SkyWest at 275.

United has scrapped 258 flights so far, with some cancellations extending to Saturday as it awaits regulatory nod to resume operating Boeing's 737 MAX 9 jets.

The carrier said in a statement that it was operating 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.