US President Joe Biden has issued an emergency declaration for Mississippi, making federal funding available to Carroll, Humphreys, Monroe and Sharkey counties, the areas hardest hit by a deadly tornado that ripped through the Mississippi Delta on Friday night.

The announcement came as search and recovery crews resumed the daunting task of digging through the debris of flattened and battered buildings on Sunday after at least 25 people were killed, dozens of others injured and hundreds displaced.

The massive storm left a trail of devastation in one of the poorest regions of the US as it tore through several towns on its hour-long path.

One man died when his trailer home flipped several times in Alabama.

Read More: Denial of democracy? Macron will pay a high price for pensions meltdown

The twister flattened entire streets, obliterated houses, ripped a steeple off a church and toppled a municipal water tower.

Even with recovery just starting, the National Weather Service warned of the risk of further severe weather on Sunday – including high winds, large hailstones and possible more tornadoes – in eastern Louisiana, south central Mississippi and south central Alabama.

Based on early data, the tornado received a preliminary EF-4 rating, the National Weather Service office in Jackson said in a tweet late on Saturday.

An EF-4 tornado has top wind gusts between 166mph and 200mph, according to the service. The Jackson office warned it is still gathering information on the tornado.

President Joe Biden promised federal help to Mississippi, and Deanne Criswell, administrator of the Federal Emergency Management Agency, was scheduled to visit on Sunday to evaluate the destruction.

The tornado on Friday night devastated a swathe of the 2,000-person town of Rolling Fork, reducing homes to piles of rubble, flipping cars on their sides and toppling the town’s water tower.

Other parts of the Deep South were digging out from damage caused by other suspected twisters.

One man died in Morgan County, Alabama, the sheriff’s department there said in a tweet.

“How anybody survived is unknown by me,” said Rodney Porter, who lives 20 miles (32km) south of Rolling Fork.

When the storm hit on Friday night, he immediately drove there to assist in any way he could.

He arrived to find “total devastation” and said he smelled 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.

Annette Body drove to the hard-hit town of Silver City from nearby Belozi to survey the damage.

She said she was feeling “blessed” because her own home was not destroyed, but other people she knows lost everything.

“Cried last night, cried this morning,” she said, looking around at flattened homes.

Read More: Lord Advocate's failed fraud case against former Rangers finance chief was malicious

“They said you need to take cover, but it happened so fast a lot of people didn’t even get a chance to take cover.”

Storm survivors walked around on Saturday, many dazed and in shock, as they broke through thickly clustered debris and fallen trees with chainsaws, searching for survivors.

Power lines were pinned under decades-old oaks, their roots torn from the ground.

Mississippi Governor Tate Reeves issued a state of emergency and vowed to help rebuild as he viewed the damage in a region dotted with wide expanses of cotton, corn and soybean fields and catfish farming ponds.

He spoke with President Biden, who also held a call with the state’s congressional delegation.

More than half a dozen shelters were opened in Mississippi to house those who have been displaced.

Preliminary information based on estimates from storm reports and radar data indicate the tornado was on the ground for more than an hour and traversed at least 170 miles (274km), said Lance Perrilloux, a meteorologist with the National Weather Service’s office in Jackson, Mississippi.

“That’s rare – very, very rare,” he said, attributing the long path to widespread atmospheric instability.

Mr Perrilloux said preliminary findings showed the tornado began its path of destruction just south-west of Rolling Fork before continuing north-east towards the rural communities of Midnight and Silver City and onwards toward Tchula, Black Hawk and Winona.

The supercell that produced the deadly twister also appeared to produce tornadoes causing damage in north-west and north-central Alabama, said Brian Squitieri, a severe storms forecaster with the weather service’s Storm Prediction Centre in Norman, Oklahoma.