US, Jan 12 (Reuters) - Airlines in the United States canceled more than 2,000 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 2,058 flights were canceled and 5,846 flights were delayed as of 5.30 p.m. ET, according to flight-tracking website FlightAware.

Southwest Airlines (LUV.N) led the list of cancellations with 401 flights, followed by SkyWest (SKYW.O) at 358.

"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 (DAL.N) said.

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.

United has scrapped 284 flights so far, with some cancellations extending to Saturday as it awaits regulatory nod to resume operating Boeing's (BA.N) 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 (ALK.N) flight last week in mid-air, forcing an emergency landing.