Millions of people hunkered down in a deep freeze overnight and early morning to ride out the frigid storm that has killed at least 18 people across the United States, trapping some residents inside homes and knocking out power to hundreds of thousands of homes and businesses.

The scope of the storm has been nearly unprecedented, 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.