At least 14 tornadoes touched down in Mississippi, killing at least three people as the system raced through the state for more than half an hour for 100 miles or so, from the Mississippi River to the northern part of the state and further into Tennessee. Authorities said the victims included a 7-year-old boy, killed when a tornado picked up and tossed a car he was in with relatives.
According to the Tennessee Department of Health, a man and a woman died when severe storms hit Perry County.
Officials said they expected to learn of more fatalities.
High winds were expected to continue overnight, with the possibility of isolated tornadoes.
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The threat of severe weather just before Christmas is unusual, but not unprecedented, said Greg Carbin, a meteorologist at the national Storm Prediction Center. On Christmas Day in 2012, a storm system spawned several tornadoes, damaging homes from Texas to Alabama.
The Associated Press contributed to this report.