Killer tornadoes in US leave 20 dead

A new round of twister tornadoes ripped through South US killing five people in Mississippi and Alabama a day after another storm left a trail of destruction in Arkansas.

At least 15 people were killed by Sunday's storms in Arkansas where emergency officials searched for survivors in the debris left by a powerful tornado that carved in 80-mile path of destruction through suburban Little Rock, media reports said.

As Alabama Governor Robert Bentley Monday declared a state of emergency for all counties, Arkansas Governor Mike Beebe said the storm was one of the worst to hit the state in recent memory.

Mississippi Governor Phil Bryant said the twisters inflicted "severe damage" around the town of Louisville, about 90 miles northeast of Jackson, and more around Tupelo, CNN reported.

Winston Medical Centre, Louisville's major hospital, was among the buildings hit, Bryant told reporters.

The National Weather Service issued a tornado emergency warning for the area around Athens, Alabama, near the Tennessee state line, on Monday evening, CNN said.

A tornado emergency also was declared in southeastern Tennessee for east central Lincoln, Moore and northwest Franklin counties.

Storm spotters were tracking a large and extremely dangerous tornado seven miles east of Fayetteville, Tennessee, the weather service said.

The National Weather Service's Storm Prediction Centre declared tornado emergencies for several counties in northern Mississippi on Monday afternoon as the line of storms moved through the state from southwest to northeast.

Nearly 5 million people were at moderate risk of severe weather late Monday, while 31 million people were at slight risk, including those in Atlanta and Nashville, CNN said.

The Arkansas tornado was the largest of several produced by a powerful storm system that rumbled through the central and southern US, according to CBSNews.