A severe cold wave continued to sweep across much of the United States on Monday, as a polar storm claimed at least 11 lives, knocked out power to more than one million homes, and forced the cancellation of thousands of flights.

According to Agence France-Presse (AFP), authorities warned that a polar air mass would keep temperatures at extremely low levels for several more days.

States of emergency were declared in around 20 states, as well as in the federal capital, Washington, D.C.

The National Weather Service said the storm is considered by some experts to be among the worst winter storms the United States has experienced in recent decades, bringing freezing temperatures, heavy snowfall, and widespread ice accumulation that could lead to severe consequences.