(CNN) -- The death toll from a wave of violent storms that swept across the South skyrocketed to 173 after county-by-county reviews by Alabama and Mississippi emergency management agencies Thursday turned up scores of additional fatalities that more than doubled the total, officials said.
The vast majority of fatalities occurred in Alabama, where at least 128 people perished, Jennifer Ardis, a spokeswoman for Gov. Robert Bentley, told CNN Thursday. A breakdown provided by Ardis showed that violent weather claimed lives in 16 Alabama counties. The hardest hit was DeKalb County, Alabama, where 30 people perished in the storms.
Before dawn Thursday, Mississippi emergency management officials also added 14 previously unreported fatalities to the count, increasing the death toll in that state to 32, officials said.
The storms left fatalities in five southern states, including Arkansas, Georgia and Tennessee. They leveled neighborhoods and left hundreds of thousands of customers without power throughout the region.
"This could be one of the most devastating tornado outbreaks in the nation's history by the time it's over," CNN Meteorologist Sean Morris said.
Long before the death toll mushroomed, governors in Alabama, Mississippi and Georgia had declared states of emergency within their borders.
President Barack Obama announced late Wednesday he had approved Bentley's request for emergency federal assistance, including search and rescue support.
"While we may not know the extent of the damage for days, we will continue to monitor these severe storms across the country and stand ready to continue to help the people of Alabama and all citizens affected by these storms," Obama said in a statement.
At least one strong tornado swept through Tuscaloosa, Alabama, leaving dozens of roads impassable and destroying hundreds of homes and businesses.
"It literally obliterated blocks and blocks of the city," Mayor Walter Maddox said, describing Tuscaloosa's infrastructure as "decimated."
Witnesses also reported tornado touchdowns in Birmingham, Alabama.
"It looked like it was probably a mile wide," Birmingham Mayor William Bell said.
The northwest corner of the city was particularly devastated, he said, with hundreds injured and many others missing.
Red Cross spokesman Chris Osborne said the number of ambulances on the street in Birmingham, "is just like taxicabs in New York."
"It's just back and forth to area hospitals," Osborne said. "It's really just an incredible sight to see."
Osborne said Pratt City and Pleasant Grove were among the hardest hit areas.
"It's just bare land, debris everywhere," Cierra Brown, of Jefferson County, Alabama, told CNN affiliate WBMA about her devastated neighborhood. "There's no house."
"My bathroom is across the street," Talesha Oliver told WBMA.
Henry Nguyen told CNN early Thursday he was working at his father's convenience store on the edge of Pratt City when he saw a twister angling for the front door. He ducked. When he stood up, Nguyen said he saw that the tornado had missed the storefront by 50 yards.
"Houses are gone. It's pretty crazy," Nguyen said. "A gas station up the street is gone. There is nothing else open here."
Several meteorological conditions combined Wednesday to create a particularly dangerous mix, CNN's Morris said.
"It is tornado season, but an intensive event like this only will occur maybe once or twice a year," he said. "It's very rare to have all these ingredients come together."
Reports of people trapped in homes or overturned vehicles were coming in from every state in the region, according to emergency management officials.
At least 32 people were killed in storm-related incidents in Mississippi on Tuesday night and Wednesday, according to the state Emergency Management Agency. Among the fatalities was a 3-year-old girl in McComb, Mississippi, who died in her bed from a falling tree.
"Our thoughts and prayers are with the families who lost loved ones or property in this devastating storm," said Mississippi Gov. Haley Barbour, who declared a state of emergency in 39 counties. The declaration allows the state to offer aid to the counties during recovery efforts.
The state was also bracing for flooding along the Mississippi River.
The storms killed 11 people in Georgia. Seven were killed in Catoosa County and two in Dade County, according to the Georgia Emergency Management Agency. The storms claimed two additional victims in Spalding County, according to the local sheriff's office.
The town of Ringgold, Georgia, was hit particularly hard.
The storm also unleashed as many as 80,000 chickens in Pickens County, Georgia, after four of their houses were destroyed.
Georgia Gov. Nathan Deal declared disaster areas and states of emergency in four other northwestern counties -- Catoosa, Floyd, Dade and Walker.
Arkansas and Tennessee reported that at least one person died in each of those states.
-- CNN's Anna Rhett Miller, John Branch, Stephanie Gallman, Maria White, Vivian Kuo, Sean Morris, Dave Alsup, John Murgatroyd, Phil Gast, Tommy Andres and Scott Thompson contributed to this report.
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