The -mile wide tornado roared across at least three counties in west-central Mississippi. Mayor McArthur Straughter said the county coroner confirmed the deaths.
"It's devastating. All of the buildings up in this area have had the roof torn off," said Straughter, estimating about 15 to 20 buildings had been heavily damaged.
Power lines and trees were down, blocking roads, Straughter said by telephone as sirens whined in the background. At least four people had been brought by four-wheeler to a triage center at an old discount store parking lot in the town about 40 miles north of Jackson.
Three counties were conducting a "massive response," Mississippi Emergency Management Agency spokesman Greg Flynn said.
Jim Pollard, a spokesman for American Medical Response ambulance service, said the company dispatched 11 ambulances to Yazoo City. He confirmed one person with significant injuries was airlifted to a Jackson hospital. He said at least four people were taken to hospitals by ambulance.
Willie M. Horton, 78, said he hunkered down in the hallway of his house in rural Holmes County. "Everything is down. A lot of trees. Big trees," Horton said.
He said his sister-in-law's house nearby was damaged, and a nephew's mobile home was carried away by the storm.
"My cousin - half his barn is gone," Horton said.
The severe storms swept across the Southeast, darkening skies and dumping rain on the region. Many areas were under tornado watches or warnings at some point during the day.
The weather hampered crews trying to clean up an oil spill after an offshore rig exploded earlier this week off the coast of Louisiana. Several sporting events and festivals were also rescheduled.
In Mississippi, the tornado struck Valley Park, Yazoo City and Durant, said Mark McAllister, a meteorologist for the National Weather Service in Jackson.
"Everything is closed off. It's hard to get emergency personnel in there," he said.
The storms also damaged a church in east-central Mississippi and caused minor damage at Olive Branch Middle School in DeSoto County, just south of Memphis, Tenn. A possible tornado was reported in Alabama, damaging homes and downing trees but causing no injuries.
In Louisiana, storms damaged a tank at a chemical plant near Tallulah. Louisiana State Police Sgt. James Martin says plant officials don't know of any chemicals leaking from the plant itself.