Several tornadoes cut across northern Alabama on Monday, NBC News reported. At least two people were killed in the town of Athens, the network said.
A tornado also swept through the northern Mississippi city of Tupelo around 2.30 pm (1930 GMT), the National Weather Service said, adding that a crew was en route to survey damage.
Parts of Alabama were also at high risk of severe storms, with a moderate risk affecting portions of Louisiana, Tennessee and Mississippi as the system travelled east, with numerous tornadoes expected.
The National Weather Service said more than 49 million people living in the watch areas were threatened by the storms, upwards of 1.4 million of them in high-risk areas.
In the hardest-hit parts of Arkansas, emergency crews intensified their search for survivors of Sunday’s twisters, as residents of the close-knit community of Vilonia surveyed the damage.
Dozens of Arkansas National Guard troops were assisting local authorities with medical evacuations, fresh water deliveries and search and rescue operations.
Vilonia police chief Brad McNew said the town of 4,000 had been rendered unrecognizable.
“It’s houses completely down to the foundations,” he told NBC television.
Through the night, rescuers used searchlights in blacked-out areas, sifting through mountains of rubble in the hopes of finding someone alive.
The Arkansas Department of Emergency Management said 14 people had been killed in the state – an earlier figure of 15 was revised as one victim was counted twice – while an official in Oklahoma state said there were at least two tornado victims there.
Local media reported another fatality in the state of Iowa.
McNew said more would have been killed if not for emergency sirens that warned people the twister was about to hit.
“I went to a tornado shelter myself with my family which was a couple miles away from where we were at. A lot of people in the community were there. And so, it did work,” he said.