Washington (AFP) - At least 23 people were killed as a devastating tornado ripped across the southern US state of Mississippi, tearing off roofs, smashing cars and flattening entire neighborhoods.

The powerful storm system, accompanied by thunderstorms and driving rain, cut a path of more than 100 miles (60 kilometers) across Mississippi late Friday, slamming several towns along the way.

The state's emergency management agency said Saturday that at least four people were missing and dozens more were injured, while tens of thousands of people in Mississippi, Alabama and Tennessee were without power.

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 were ripped up and trees uprooted, television footage showed.

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

Resident Shanta Howard described to local TV how residents 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.

Search and rescue operations were underway in Sharkey county, home to Rolling Fork -- located about 70 miles northwest of the state capital Jackson -- and neighboring counties.

Officials cautioned that the death toll could rise from 23.

"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.

'Constant cry' for help

Storm chaser Aaron Rigsby told AFP he arrived in Rolling Fork right after the storm hit, in the pouring rain and with "lightning still all around."

"When I got there, it was just a constant cry of voices screaming for help from people that were trapped," he said, adding he helped residents to free a few people from their destroyed homes.

The National Weather Service issued a rare tornado emergency for Rolling Fork and surrounding areas at 9:00 pm Friday, warning people to seek shelter from life-threatening conditions and forecasting golf ball-sized hail.

The tornado watch expired in the early hours of Saturday, meteorologists said. More thunderstorms were expected, but they were not forecast to be severe.

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.

The NWS warned residents that as clean-up operations continue, "dangers remain even after the storms move on."

Malary White, a spokeswoman for the Mississippi Emergency Management Agency, said officials would fully assess the damage throughout Saturday.

"Our main priority right now, especially for the local first responders, it's life safety and accounting for the people and making sure they are safe," she told CBS News affiliate WJTV.

"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."

Tornadoes, a weather phenomenon notoriously difficult to predict, are relatively common in the United States, especially in the central and southern parts of the country.

In January, a series of damaging twisters, all on the same day, left several people dead in Alabama and Georgia.