The death toll from a historic outbreak of tornadoes across the South has risen to more than 300, though officials say the definitive toll may not be known for days. The deadly storms have also injured hundreds and destroyed entire neighborhoods, leaving many in the region homeless.

The state of Alabama has been hit the hardest by the storms, with at least 200 deaths reported. Alabama Gov. Robert Bentley said on Thursday that he expected the death toll in his state to climb.

"We do expect that number to rise," Alabama Gov. Robert J. Bentley said. "This may be the worst natural disaster in Alabama's history."

In Alabama, the college town of Tuscaloosa was particularly devastated by a massive tornado that swept through the area.

The Los Angeles Times reported:

Parts of Tuscaloosa, a town of about 93,000 that is home to the University of Alabama, were unrecognizable at daybreak Thursday. Storm chasers captured the immense, gray funnel cloud on video, a terrifying column that seemed to fill the sky.

"The amount of damage that is seen is beyond a nightmare," Tuscaloosa Mayor Walter Maddox said after touring the city by air. The tornado, he said, wiped out a three- to four-mile long stretch of the town. The swath was about half a mile wide in places.

"I don't know how anyone survived," Maddox told reporters. He said some neighborhoods had been "removed from the map…. There are parts of this city I don't recognize, and that's someone that's lived here his entire life."

President Obama declared a state of emergency in Alabama. He will visit the state on Friday to survey the devastation, meet with government officials and those affected by the storm.

Meanwhile, parts of he South are also bracing for another possible disaster, as the Mississppii River has risen to a level not seen since the Great Mississippi Flood of 1927. The Governors of Mississippi and Louisiana issued flood warnings Thursday while also declaring states of emergency. Authorities in both states are warning residents along the waterway to prepare for the possibility of flooding. 

"We're going to do everything we can to prepare for the worst-case scenario while we still are hoping for the best case," Louisiana Gov. Bobby Jindal said. Jindal, whose state is still recovering from the flooding and destruction left by Hurricane Katrina more than five years ago, said his state is prepared to withstand the test.

The Huffington Post reported: "The river is forecast to crest at 53.5 feet on May 18 at Vicksburg, Miss., a key gauge. That is the highest river stage recorded at Vicksburg since the catastrophic flooding of 1927 when the river reached 56.6 feet and would have kept on rising if levees hadn't given way, causing massive flooding and killing hundreds. After that calamity, the nation undertook an aggressive $13 billion plan to build levees and floodways that would avert such a scale of flooding again."