The rare December twisters that flattened houses and caused chaos on highways raised the death toll from days of deadly weather across the South to at least 28.
An infant was reportedly among the latest casualties.
The extreme weather, fueled by unseasonably warm air, is likely to continue for the next few days, the National Weather Service warned, complicating search and rescue efforts and possibly wreaking more havoc on the region.
Several tornadoes touched down around the densely populated Dallas area Saturday evening, the day after Christmas, with the city of Garland to the northeast the hardest hit.
Aerial footage taken as day broke showed some homes completely flattened, while others had roofs blown off and windows shattered, curtains fluttering in the wind.
"It is total devastation," local police spokesman Lt Pedro Barineau was quoted as saying by the Dallas Morning News.
It was here that authorities confirmed eight fatalities, adding that 15 people were taken to hospital with injuries.
About 600 buildings have been damaged, they said, with single-family homes most affected.
"Officials are continuing this morning to check and clear structures as they assess the damage in the approximate 2-square-mile (five-square-kilometer area) area," officials said in a statement.
Police said the deaths happened during tornado-related traffic accidents near Interstate 30 and the George Bush Turnpike, the Dallas Morning News reported, saying some of the bodies were found in cars while others were catapulted from the scene.
Three other storm-related fatalities occurred in the towns of Copeville and Blue Ridge in Collin County to the northeast of Dallas, the local sheriff's office confirmed to AFP, without providing more details.
The Dallas Morning News reported that an infant was among the dead.
Dangerous weather to continue
The late Saturday deaths in Texas came as millions of residents in the southern United States struggle to recover from fierce storms and heavy flooding, with more rain in the forecast.
At least 17 people were killed in storm-related incidents since Wednesday in Mississippi, Tennessee and Arkansas, local officials said.
In Alabama, heavy flooding continued on Sunday following several days of heavy rain that began on Thursday.
Governor Robert Bentley declared a state of emergency to deal with the flooding just before tornadoes uprooted trees and tore off rooftops on Christmas Day.
One touched down in Birmingham, the state's most populous city. There were no fatalities, but the twister damaged three homes, local fire chief Charles Gordon told CNN.
Near the state capital Montgomery, more than 300 inmates at the minimum-security Red Eagle Community Work Center were forced to evacuate due to flooding, local media reported.
And residents of the town of Elba were nervously eyeing a levee amid forecasts that the Pea River would crest and possibly overflow the barrier, the AL.com news site reported.
In Mississippi, where Governor Phil Bryant declared a state of emergency to deal with flooding, "severe storms" are forecast for late Sunday through Monday, the state Emergency Management Agency said.
Early EMA damage reports showed 241 homes destroyed or with major damage, and more than 400 total homes affected.
The agency confirmed the deaths of 10 people in Mississippi. There were another six confirmed fatalities in Tennessee, and one person was killed in Arkansas.
Georgia Governor Nathan Deal also declared states of emergency in counties affected by the weather.
"A variety of dangerous weather conditions will continue across the middle of the country through Sunday," the National Weather Service said.
It warned of "blizzard conditions" from west Texas into Kansas, and "hazardous ice accumulations" in Oklahoma.
"Dangerous flooding will extend from north Texas to central Illinois," it said.
Flood warnings and advisories also remained in effect in parts of Mississippi, Tennessee, Alabama, Kentucky and other areas in the southeast.
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