TUSCALOOSA, Ala. - Southerners found their emergency safety net shredded Friday as they tried to emerge from the second-deadliest day for a twister outbreak in US history.

Cars destroyed by a tornado are left in Pleasant Grove, Alabama, April 29, 2011. President Barack Obama promised federal aid on Friday to the tornado-ravaged US South after he got a close-up look at the "heartbreaking" impact of deadly twisters that occurred on April 27, killing at least 337 people.  [Photo/Agencies]

Emergency buildings are wiped out. Bodies are stored in refrigerated trucks. Authorities are begging for such basics as flashlights. In one neighborhood, the storms even left firefighters to work without a truck.

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The death toll from Wednesday's storms reached 337 across seven states, including at least 246 in Alabama.

The largest death toll ever was on March 18, 1925, when 747 people were killed in storms that raged through Missouri, Illinois and Indiana. The second deadliest day had been in March 1932, when 332 people died, all in Alabama.

The 1925 outbreak was long before the days when Doppler radar could warn communities of severe weather. Forecasters have said residents were told these tornadoes were coming. But they were just too wide and powerful and in populated areas to avoid a horrifying body count.

Hundreds if not thousands of people were injured Wednesday - 990 in Tuscaloosa alone - and as many as 1 million Alabama homes and businesses remained without power.

The scale of the disaster astonished US president Barack Obama when he arrived in the state Friday.

"I've never seen devastation like this," he said, standing in bright sunshine amid the wreckage in Tuscaloosa, where at least 45 people were killed and entire neighborhoods were flattened. Hours later, Obama signed disaster declarations for Mississippi and Georgia, in addition to one he had authorized for Alabama.

Tuscaloosa Mayor Walt Maddox called the devastation "a humanitarian crisis" for his city of more than 83,000.

Maddox said up to 446 people were unaccounted for in the city, though he added that many of those reports probably were from people who have since found their loved ones but have not notified authorities. Cadaver-detecting dogs were deployed in the city Friday but they had not found any remains, Maddox said.

During the mayor's news conference, a man asked him for help getting into his home, and broke down as he told his story.

"You have the right to cry," Maddox told him. "And I can tell you, the people of Tuscaloosa are crying with you."

Friday night, Tuscaloosa officials reduced downward the death toll for the city and its police jurisdiction by six to 39, still the most in Alabama. With that change factored in, the state's death toll stood at 246 early Saturday.

At least one tornado - a 205 mph monster that left at least 13 people dead in Smithville, Miss. - ranked in the National Weather Service's most devastating category, EF-5. Meteorologist Jim LaDue said he expects "many more" of Wednesday's tornadoes to receive that same rating, with winds topping 200 mph.

Tornadoes struck with unexpected speed in several states, and the difference between life and death was hard to fathom. Four people died in Bledsoe County, Tenn., but a family survived being tossed across a road in their modular home, which was destroyed, Mayor Bobby Collier said.