At least 25 people were killed and dozens injured as tornadoes and strong thunderstorms swept across Mississippi late on Friday, leaving a trail of damage more than 160 kilometres long.
The National Weather Service said a tornado caused damage for nearly 100 kilometres north-east of Jackson, sweeping through the rural towns of Silver City and Rolling Fork at 113 kph without weakening and racing towards Alabama.
“How anybody survived is unknown by me," Mississippi resident Rodney Porter told the AP.
As the storm hit Friday night, he immediately drove over 30 kilometres towards the devastation to render aid. Upon his arrival he found “total devastation” and said he smelled natural gas and heard people screaming for help in the dark.
“Houses are gone, houses stacked on top of houses with vehicles on top of that,” he said.
Photographs of the destruction showed entire buildings left in rubble and cars turned over on their sides as people climbed through the debris in darkness.
President Biden called the images from Mississippi "heartbreaking".
"We will do everything we can to help. We will be there as long as it takes," he said in a statement.
The Mississippi Emergency Management Agency said there were 25 confirmed deaths by Saturday afternoon.
The agency said four people were missing as search and rescue teams combed through the destruction looking for survivors in Silver City.
Search and rescue teams were also out in Rolling Fork, which bore the brunt of the tornado, CNN reported.
"My city is gone," Rolling Fork Mayor Eldridge Walker told CNN. "Devastation — as I look from left to right, that's all I see.
"A lot of families are hurting. This community is in a situation that we never expected.
"Houses that are torn up can be replaced but we can't replace a life."
The National Weather Service received at least 24 reports of tornadoes overnight from storm chasers and observers.
The agency had issued an alert urging people to take cover before the bad weather struck.
“You are in a life-threatening situation,” it warned. "Flying debris may be deadly to those caught without shelter. Mobile homes will be destroyed. Considerable damage to homes, businesses, and vehicles is likely and complete destruction is possible."
Mississippi tornadoes and storms leave at least 25 dead
Meanwhile, US President Joe Biden on Sunday approved an emergency declaration for the state, ordering supplemental federal aid for state, tribal and local recovery efforts in the affected areas, a White House statement said.
The funding will provide grants for temporary housing, home repairs and low-cost loans to cover uninsured property losses, read the statement.
Mississippi Governor Tate Reeves assured residents in a Twitter post on Saturday that federal help was on the way.
"I just spoke with President Biden about the deadly tornados we faced overnight. He assured us FEMA would be there to support our response. The flood of support from governors, businesses, charities, and federal admin has been tremendous — matches the community here on the ground," his post read.
Pope Francis offered a special prayer for the people of Mississippi “hit by a devastating tornado” during his weekly noon blessing overlooking St Peter’s Square in Vatican City on Sunday.
At least two people died in Missouri as severe weather hit other areas of the southern US. A suspected tornado touched down early on Friday in Texas, damaging homes and downing trees and power lines.
Some parts of southern Missouri received nearly 8 centimetres of rain between Thursday night and Friday morning. A car carrying six young adults was swept away and two passengers drowned as it tried to cross a bridge over a flooded stream in the town of Grovespring.
The National Oceanic and Atmospheric Administration’s Storm Prediction Centre said Arkansas, Louisiana, Mississippi and Tennessee faced the greatest threat of tornadoes. Storms with damaging winds and hail were forecast from eastern Texas and south-eastern Oklahoma into parts of south-eastern Missouri and southern Illinois.