Airlines cancel 5,700 US flights amid fierce winter storms

Airline cancellations topped 5,700 US flights on Friday as massive winter storms snarled airport operations around the United States and frustrated tens of thousands of holiday travellers.

That followed nearly 2,700 cancelled flights on Thursday, while just over 1,000 flights have already been cancelled for Saturday, according to flight tracking website FlightAware.

Passenger railroad Amtrak has cancelled dozens of trains through Christmas, disrupting holiday travel for thousands.

Highways in the Midwest faced lengthy delays because of snowy weather or crashes, and authorities in parts of Indiana, Michigan, New York and Ohio urged motorists to avoid nonessential travel.

The Federal Aviation Administration (FAA) imposed ground stops or delays for de-icing at several US airports because of winter weather.

Transportation Secretary Pete Buttigieg told CNN the US aviation system "is operating under enormous strain" with two different storms and high winds affecting airports around the country. Buttigieg said about 10 per cent of US flights were cancelled on Thursday.

Another 10,400 US flights were delayed on Friday - including more than 40 per cent of those operated by American Airlines, United Airlines, Delta Air Lines and Southwest Airlines - after 11,300 flights were delayed Thursday.

Southwest cancelled 1,238 flights on Friday, 29 per cent of all its scheduled flights, while Alaska Airlines ALK.N cancelled 507, or 64 per cent of its flights.

Seattle-Tacoma International Airport had 357 flights, or 63 per cent of departures, cancelled Friday. The FAA lifted a ground stop there due to snow and ice, but late Friday delays still averaged nearly three hours.

Nearly half of departing flights at Detroit Metro were cancelled, along with 70 per cent at Portland, 38 per cent at New York's LaGuardia, 29 per cent at Chicago O'Hare and 27 per cent at Boston.