Washington, Apr 25 (DPA): Seven people died Saturday when a huge tornado scrubbed Louisiana and Mississippi with 240-km-an-hour winds, Mississippi officials said.

"There's untold damage," Greg Flynn of Mississippi Emergency Management services told CNN.

The storm system that delivered the twister spawned at least another 40 tornadoes across a broad swath of the US south and mid-west, including Missouri, Tennessee, Alabama, Georgia, Arkansas, Kentucky and Indiana.

Sunday, the system was expected to carry heavy thunderstorms, hail and a few tornadoes east toward Virginia, North Carolina, South Carolina, Georgia and Florida, AccuWeather said.

The National Weather service warned of a "particularly dangerous situation".

"Seek shelter immediately if you hear thunder," AccuWeather warned.

People "must be underground" to stay safe, urged the CNN weather expert.

The 1.2-km-wide lethal twister killed seven people, including two children, as it touched down in Louisiana, scrubbed across Yazoo City, Mississippi, on the Mississippi River Delta, and pushed eastward across Mississippi.

Parts of Yazoo City, the hometown of Mississippi Governor Haley Barbour, were "obliterated", Flynn said.

Dozens of people were injured.

"Churches have been obliterated. Trees and power lines are down, and rescue crews can't get in," Barbour said in broadcast comments.