An arctic cold snap continued to grip a large swath of the United States on Monday, as a major winter storm killed at least 11 people, left more than a million households without power, and grounded thousands of flights. Authorities warned that a mass of arctic air would keep dangerously low temperatures in place for several days.

A state of emergency was declared in about 20 states as well as in Washington, DC. The death toll was already heavy: In New York City, Mayor Zohran Mamdani said during a press conference on Sunday that five people had been found dead outdoors over the weekend. In Texas, officials confirmed three deaths, including a 16-year-old girl killed in a sledding accident. Two people died from hypothermia in Louisiana. In southeastern Iowa, a winter weather-related crash left one person dead and two injured on Saturday, according to local police.

About 820,000 customers were still without electricity as of Monday morning, mainly in the southern part of the country, according to the specialist website PowerOutage.com. In Tennessee, where ice brought down power lines, more than 250,000 households remained without power, while 100,000 customers in Louisiana and Mississippi were also affected.

From Texas to North Carolina, and up through New York, authorities urged residents to stay home. In the Great Plains and other central regions, the cold was expected to persist for a week, with wind chills dropping to -45°C, a potentially life-threatening level.