At least 25 people were killed by devastating tornadoes that ripped across the southern US state of Mississippi, tearing off roofs, smashing cars and flattening entire neighborhoods, with the region readying for more severe weather Sunday.

The powerful weather system, accompanied by thunderstorms and driving rain, cut a path of more than 60 kilometers across the state late Friday, slamming several towns along the way.

Mississippi's emergency management agency put the death toll at 25, and said dozens more were injured. Four people reported missing "have been found," it added.

And in Alabama, one man died after being trapped when a trailer overturned in the severe weather, the sheriff's office in Morgan County said on Twitter.

In Rolling Fork, home to fewer than 2,000 people, an entire row of houses and buildings was demolished, leaving only scattered debris. Cars were overturned, fences ripped up and trees uprooted.

Some 4,800 customers were without power in Mississippi, and nearly 11,000 homes and businesses remained in the dark in neighboring Alabama, monitor poweroutage.us reported.

Mississippi was meanwhile girding for more turbulent weather Sunday, including damaging winds and hail, with the state's emergency management agency warning that "tornadoes cannot be ruled out."

Patricia Perkins, who works at a hardware store in Rolling Fork, told AFP that "most everything is wiped away."

Resident Shanta Howard described to local TV how members of the community had to help remove the dead from the wreckage.

"It's way worse than I thought. All of the businesses on Highway 61 are gone," Ricky Cox, whose seed supply store was wrecked, told AFP, saying two friends died when their homes were hit.

"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."

Search and rescue operations were underway in Sharkey County, home to Rolling Fork and neighboring counties.

Fatalities also occurred in Humphreys, Carroll and Monroe counties, the emergency management agency said.

"The loss will be felt in these towns forever," state Governor Tate Reeves said on Twitter. "Please pray for God's hand to be over all who lost family and friends."

President Joe Biden called the images from Mississippi "heartbreaking" and vowed to put federal resources at the state's disposal.

"We will do everything we can to help. We will be there as long as it takes," he said in a statement.