At least 23 people have died after a tornado tore through the US state of Mississippi on Friday night.
More people are thought to be trapped under the rubble of destroyed buildings.
The twister caused devastation in several rural towns, where trees and power lines were torn down and tens of thousands of power outages were reported.
Several other southern states are also braced for powerful storms.
Hail the size of golf balls and heavy rainfall were reported in several areas of the state.
It is not yet clear whether one or several tornadoes hit the area. Although yesterday the National Weather Service warned that several tornadoes were forecast, it's possible the devastation was caused by a "skipping tornado" - a single twister that lifts from the surface only to touch down again.
Residents of Rolling Fork, a small town town in western Mississippi, said that a tornado blew the windows out of the back of their homes. The damage in the area is reported to be particularly bad.
Local resident Brandy Showah told CNN: "I've never seen anything like this... This was a very great small town, and now it's gone."
Cornel Knight told the Associated Press that he, his wife and their three-year-old daughter were at a relative's home in Rolling Fork and that it was "eerily quiet" just before the tornado struck. He said the sky was dark but "you could see the direction from every transformer that blew".
He said the tornado struck another relative's house, where a wall collapsed and trapped several people inside.
Other people were trapped in piles of rubble, while some law enforcement units are unaccounted for in the county of Sharkey.
Sam Emmerson from the School of Meteorology at the University of Oklahoma said that the "extremely high-calibre" tornado lofted debris above 30,000ft (9144m).
One local weather forecaster, concerned at the strength of a tornado about to hit the town of Amery, momentarily paused his TV forecast to offer a prayer for the residents of the town.
Mississippi's governor, Tate Reeves, said on Twitter that search and rescue teams were providing medical support to those affected.
"Many in the MS [Mississippi] Delta need your prayer and God's protection tonight. Watch weather reports and stay cautious through the night, Mississippi!", Mr Reeves wrote.
As Mississippi woke up to the devastation on Saturday morning, the National Weather Service said that clean up was already underway but warned people to stay far away from damaged power lines and not enter damaged buildings or walk through floodwaters.