Hundreds of flights were canceled to and from Chicago's busy airports Friday, disrupting air travel across the country as an arctic storm dumped heavy snow in the region.
As of 3.30 pm (2130 GMT) a total of 700 flights had been canceled at Chicago's O'Hare International Airport -- the second busiest in the country after Atlanta -- and Midway International Airport.
Both airports reported "significant delays and cancelations," the Chicago Department of Aviation said.
O'Hare is a major hub for United Airlines and American Airlines, two major US carriers, while Midway is used by low-cost carrier Southwest Airlines.
The greater Chicago area, home to nearly 10 million people, was under a winter storm warning Friday until midnight as a storm moving from the central United States pounded the region with snow, sleet and freezing rain.
The city's full fleet of around 280 snowplows was on duty, but struggled to keep the main roads clear.
Snow fell so quickly that, fearing accidents, Chicago officials ordered city buses off Lake Shore Drive, the busy highway that runs alongside Lake Michigan.
"Our snowplows have been out salting and plowing our roadways since this morning, but there are areas along our system that have begun to collect snow," Kristi Lafleur, with the busy Illinois Tollway, told the Chicago Sun-Times.
Police and firefighters reported helping scores of drivers whose cars had spun out of control in the ice, but no injuries or deaths.
In an urgent winter storm warning, the National Weather Service said snowfall totals of four to six inches [10 to 15 centimeters] can be expected in the Chicago area, "with locally higher amounts possible."
"Accumulating snow will cause significantly increased travel times, resulting in a particularly treacherous afternoon commute," the NWS said.
The especially low temperatures will make salt less effective and combine with heavy snowfall rates to make it harder for road crews to keep roads clear of snow and ice, it added, noting people should "only travel in an emergency."
Local Chicago forecasters however said there could be up to nine inches (23 centimeters) of snow by the time the storm had moved through.
The Federal Aviation Administration (FAA) reported delays at O'Hare airport averaging 1.5 hours due to snow and ice, though the Chicago Department of Aviation said the hold-ups averaged 45 minutes.
"Airlines at O'Hare have also canceled more than 600 in and out bound flights for the day," the Department said.
Some 100 flights scheduled to and from Midway airport had also been canceled, the Department said in a recorded message.
The storm was expected to move past Chicago overnight towards the east coast, affecting New York and as far south as the Washington area.