At least 350 deaths have been reported in six southern states, though that figure is expected to rise. 

The deadliest tornado outbreak, which killed 747, occurred in the Midwest states of Illinois, Indiana and Missouri in 1925. 

Alabama, which was hit the hardest by the storms, has reported at least 249 deaths as of Saturday. More than 1,700 people in the state were injured by the storm. "Our thoughts and prayers are with all the people of this state," Alabama Gov. Robert Bentley told reporters on Saturday. Bentley declared Sunday as a day of prayer across Alabama.

President Obama, who surveyed the damage from the violent weather in Alabama on Friday, will send senior officials from his administration to the disaster area this weekend in an effort to increase government assistance.

Obama has signed major disaster declarations for Alabama, Mississippi and Georgia.

This week's extreme weather in the South left a path of destruction in its way, knocking down homes and businesses and wiping out entire neighborhood. "It's not an exaggeration to say that whole communities were wiped out," Yasamie August, a spokeswoman for the Alabama Emergency Management Agency, said.

It is estimated that 10,000 homes and buildings have been destroyed. One disaster risk modeler is forecasting losses of between $2 and $5 billion worth of insured properties.

Reuters reported: "Recovery could cost billions of dollars and even with federal disaster aid it could complicate efforts by affected states to bounce back from recession."

Many are still without power and have been left without clean drinking water. ABC News reported:

The storms have destroyed or damaged power plants, power lines, gas stations and water supplies, leaving more than 1 million people without electricity. Thousands are homeless or without fuel or safe drinking water. Three nuclear power plants have shut down and are offline.

President Obama and the first lady toured the disaster area Friday in hard-hit Tuscaloosa, Ala., where 36 or more are dead. Eastern Tuscaloosa is running out of water. The mayor's office has ordered residents to conserve and to boil their tap water before drinking it until the city's water pressure can be fully restored.

According to FEMA, top Obama Administration officials who are scheduled to visit Alabama and Mississippi on Sunday include Secretary of Homeland Security Janet Napolitano, Agriculture Secretary Tom Vilsack, Housing and Urban Development Secretary Shaun Donovan and FEMA Administrator Craig Fugate.

Some 211 tornadoes have been estimated to have hit the region within a span of hours on Wednesday afternoon, including one in Smithville, Mississippi that has been preliminarily categorized as an EF-5. An EF-5 tornado is the highest classification for a tornado, and the one that went through Smithville is estimated to have packed winds peeds of over 200 miles per hour.

"It is capable of completely sweeping away one- and two-story houses, leaving nothing left but the basement itself," said James LaDue a meteorologist at the Warning Decision Training Branch. "It's also capable of turning vehicles into missiles."

LaDue said that EF-5 tornados are worse than hurricanes and can cause as much damage as the tsunami that struck Japan in March.