Massive tornado touches down in Georgia on day of dangerous storms
In Georgia, at least one massive tornado - estimated to be up to one mile wide - has already touched down, causing damage in Sumter County according to the local National Weather Service office.
"This is an emergency situation," the NWS office wrote in its warning, "To repeat, a large, extremely dangerous and potentially deadly tornado is on the ground. To protect your life, take cover now!"
There has also been damage to weather forecasting infrastructure.
The impacted region - covering parts of Georgia, Alabama, Tennessee, South Carolina and Kentucky - faced possible development of supercells throughout the day as very large hail and damaging straight-line wind appeared likely, the National Weather Service said in an advisory.
In Alabama, multiple counties were at risk of storms bringing hail, damaging winds and possible tornadoes until 9 p.m. local time.
"Large hail up to the size of baseballs and damaging winds will continue to be the dominate (sic) concerns of these storms," the service said. A tornado watch was in effect for numerous counties eastern Alabama.
The 5.7 million people who live in the Atlanta metro area should expect as much as 2-1/2 inches (6 cm) of rain throughout the day and into the evening, the service said.
The Federal Aviation Administration issued a ground stop at Hartsfield-Jackson Atlanta International Airport - slowing the flow of inbound flights - because of possible severe weather, the airport said in a Twitter message.
Dozens of school districts in Alabama and Georgia canceled classes while Alabama Governor Robert Bentley issued a state of emergency ahead of the storm front.
"Alabama is no stranger to the impact severe weather can have on communities and the devastation that can occur when the weather takes a turn for the worse," Bentley said in a statement.
The US Masters golf tournament, which takes place in Augusta, Georgia, also announced via Twitter that its course would be closed for the rest of the day.
The severe weather comes days after a powerful storm system in the Southeastern United States killed four people, including a woman who was swept away by flood waters while she called 911.
In Missouri on April 4, a fire department building and elementary school in the town of Goodman, some 300 miles (480 km) southwest of St. Louis, was extensively damaged when a tornado touched down at around 7 p.m., Mary Curry, the assistant city clerk, said by telephone.
The town's residents remained without power on Wednesday, Curry said. There was one minor injury caused by the storm.