A wild winter storm continued to envelop much of the United States on Saturday, bringing blinding blizzards, freezing rain, flooding and life-threatening cold that created mayhem for those traveling for the Christmas holiday.

The storm that arrived earlier in the week downed power lines, littered highways with piles of cars in deadly accidents and led to mass flight cancellations.

The storm was nearly unprecedented in its scope, stretching from the Great Lakes near Canada to the Rio Grande along the border with Mexico. About 60% of the U.S. population faced some sort of winter weather advisory or warning, and temperatures plummeted drastically below normal from east of the Rocky Mountains to the Appalachians, the National Weather Service said.

Freezing rain coated much of the Pacific Northwest in a layer of ice, while people in the Northeast faced the threat of coastal and inland flooding.

The frigid temperatures and gusty winds were expected to produce “dangerously cold wind chills across much of the central and eastern U.S. this holiday weekend,” the weather service said, adding that the conditions “will create a potentially life-threatening hazard for travelers that become stranded.”

“In some areas, being outdoors could lead to frostbite in minutes,” it said.

Adding to the woes were power outages that by late Friday were still affecting more than a million homes and businesses, according to the website PowerOutage, which tracks utility reports.

As millions of Americans were traveling ahead of Christmas, more than 5,700 flights within, into or out of the U.S. were canceled Friday, according to the tracking site FlightAware.

Multiple highways were closed and crashes claimed at least six lives, officials said. Four people died in a massive pileup involving some 50 vehicles on the Ohio Turnpike. A Kansas City, Missouri, driver was killed Thursday after skidding into a creek, and three others died Wednesday in separate crashes on icy northern Kansas roads.

In Canada, WestJet canceled all flights Friday at Toronto Pearson International Airport, as meteorologists there warned of a potential once-in-a-decade weather event. While in Mexico, migrants camped near the U.S. border in unusually cold temperatures as they awaited a U.S. Supreme Court decision on pandemic-era restrictions that prevent many from seeking asylum.

Forecasters said a bomb cyclone — when atmospheric pressure drops very quickly in a strong storm — had developed near the Great Lakes, stirring up blizzard conditions, including heavy winds and snow.

Even people in Florida were braced for unusually chilly weather as rare freeze warnings were issued for large parts of the state over the holiday weekend.

Activists were rushing to get homeless people out of the cold. Nearly 170 adults and children were keeping warm early Friday in Detroit at a shelter and a warming center that are designed to hold 100 people.

“This is a lot of extra people” but it wasn’t an option to turn anyone away, said Faith Fowler, the executive director of Cass Community Social Services, which runs both facilities.

Emergency weather shelters in Portland, Oregon, called for volunteers amid high demand and staffing issues as snow, freezing rain, ice and frigid temperatures descended upon the area.

South Dakota Gov. Kristi Noem said she was deploying the National Guard to haul timber to the Oglala Sioux and Rosebud Sioux tribes and help with snow removal.

“We have families that are way out there that we haven’t heard from in two weeks,” said Wayne Boyd, chief of staff to the Rosebud Sioux president.

On the Pine Ridge Indian Reservation, Harlie Young was huddled with five children and her father around a wood stove as 12-foot (3.6-meter) snow drifts blocked the house.

“We’re just trying to look on the bright side that they’re still coming and they didn’t forget us,” she said Friday.

Calling it a “kitchen sink storm,” New York Gov. Kathy Hochul declared a state of emergency. In parts of New York City, tidal flooding inundated roads, homes and businesses Friday morning.

In Boston, rain combined with a high tide, flooded some downtown streets on Friday.