A rare blast of snow, sleet and ice hit the southern United States, prompting three states to declare a state of emergency.
The winter storm also closed the New Orleans airport and caused chaos on roads for drivers unaccustomed to the dangerously slick conditions.
The southern cold snap is part of an Arctic front that has put much of the northeast and northern plains under warnings and advisories for severe wind chills.
Temperatures in parts of those regions could feel as cold as -30F (-34C), the National Weather Service said.
Louisiana, Mississippi and North Carolina each declared a state of emergency, telling motorists to stay off the roads.
A school bus overturned on its way to North Henderson High & Apple Valley Middle School in North Carolina.
"Residents should not overreact but should make plans now to ensure they are prepared for prolonged freezing conditions and icy roadways," said Mississippi Governor Phil Bryant.
The last flight left New Orleans at about 11am local time (5pm Irish time) and its Louis Armstrong International Airport was then closed to commercial traffic ahead of the predicted ice storm.
Authorities also shut the 39km Causeway Bridge, which spans Lake Pontchartrain, because of icy conditions.
Residents and tourists excited by the novelty of the conditions took photos of icicles hanging from the wrought-iron balconies of the city's historic French Quarter.
Temperatures are forecast to hit a low of 23F (-5C) in New Orleans tonight and the city could see its first snowfall in years.
"This is pretty rare in New Orleans," Mike Efferson of the National Weather Service Office in Slidell, Louisiana, said of the conditions.
"This only happens about every ten years."
Schools and government offices across a wide swath of the country were closed.
Airlines cancelled or delayed thousands of flights and officials closed roads as conditions worsened.
North Carolina and South Carolina are expected to get the most snow, while the heaviest ice accumulation was forecast from Louisiana to the Carolinas, the weather service said.