ATLANTA — A storm system forecasters called "particularly dangerous" killed four people as it swept across the country Wednesday.
Tornadoes touched down in Indiana and Mississippi, where three were killed.
A tree blew over onto a house in Arkansas, killing an 18-year-old woman and trapping a 1-year-old child inside, authorities said. Rescuers pulled the toddler safely from the home.
Authorities in Mississippi did not have details of those dead after multiple tornadoes hit the state.
In Benton County, where one death occurred, search-and-rescue crews were doing a house-by-house search to make sure residents were accounted for.
A tornado damaged or destroyed at least 20 homes in the northwest part of the state. Clarksdale Mayor Bill Luckett said the only confirmed casualty was a dog killed by storm debris. Planes at a small airport overturned and an unknown number of people were injured.
"I'm looking at some horrific damage right now," the mayor said. "Sheet metal is wrapped around trees; there are overturned airplanes; a building is just destroyed."
Television images showed the tornado appeared to be on the ground for more than 10 minutes. Interstate 55 was closed in both directions as the tornado approached, the Mississippi Highway Patrol said.
After an EF-1 tornado struck the south Indianapolis suburb of Greenwood, television stations showed pictures of damage including a portion of a roof blown off a veterinary office.
The biggest threat for tornadoes was in a region of 3.7 million people in Mississippi, Tennessee and Arkansas and parts of Missouri, Illinois and Kentucky, according to the national Storm Prediction Center in Oklahoma. The center issued a "particularly dangerous situation" alert for the first time since June 2014, when two massive EF4 twisters devastated a rural Nebraska town, killing two people.
The greatest risk for a few "intense, long-tracked tornadoes" will be through Wednesday night.
About 120 miles east of the tornado, Brandi Holland, a convenience store clerk in Tupelo, Mississippi, said people were reminded of a tornado that damaged or destroyed more than 2,000 homes and businesses in April 2014.
"They're opening all our tornado shelters because they say there's an 80 percent chance of a tornado today," Holland said.
Elsewhere, skiers on the slopes out West got a fresh taste of powder and most people in the Northeast enjoyed spring-like temperatures as they finished up last-minute Christmas shopping.
"It's too warm for me. I don't like it. I prefer the cold in the winter, in December. Gives you more of that Christmas feel," said Daniel Flores, a concierge from the Bronx, his light jacket zipped open as he shopped in Manhattan with his three children.
Only about half of the nation, mostly in the West, should expect the possibility of a white Christmas.
In the small coastal town of Loxley, Alabama, Mandy Wilson watched the angry gray sky and told drivers to be careful as she worked a cash register at Love's Travel Stop.
"It's very ugly; it's very scary," Wilson said. "There's an 18-wheeler turned over on I-10. There's water standing really bad. It's a really interesting way to spend Christmas Eve eve."
In parts of Georgia, including Atlanta, a flood watch was posted through Friday evening as more than 4 inches was expected, the National Weather Service said.
The threat of severe weather just before Christmas is unusual, but not unprecedented, said Greg Carbin, a meteorologist at the national Storm Prediction Center.
Twisters hit southeast Mississippi exactly a year ago, killing five people and injuring dozens of others. On Christmas Day in 2012, a storm system spawned several tornadoes, damaging homes from Texas to Alabama.
Emergency officials in Tennessee worried that powerful winds could turn holiday yard decorations into projectiles, the same way gusts can fling patio furniture in springtime storms, said Marty Clements, director of the Madison County Emergency Management Agency in Jackson, the state's largest city between Memphis and Nashville.
"If you go through these neighborhoods, there are a lot of people very proud of what they've put out and they've got stuff everywhere — all these ornaments and deer and everything else," Clements said. "They're not manufactured to withstand that kind of wind speed, so they become almost like little missiles."
In Arkansas, Pope County Sheriff Shane Jones said the 18-year-old woman was killed when a tree crashed into her bedroom. The woman and her 1 ½-year-old sister were sleeping in a bedroom of the house near Atkins about 65 miles northwest of Little Rock, when winds uprooted the tree that crashed through the roof.
"It's terrible that this happened, especially at Christmas," Jones said.
Forecasters said by Wednesday night, the severe weather threat could shift east into the southern Appalachian Mountain region.
Once the strong storms clear out, warm temperatures were expected. Highs in Atlanta and Charlotte, North Carolina, on Christmas Eve were forecast to be in the mid-70s.