Eleven people are reported to have been killed in tornadoes in Texas, raising the death toll to 29 in a week of storms across several US states.
At least eight people died in Garland, near Dallas, five of them when their cars were blown off a motorway. Three bodies were found in other towns.
Officials also say west Texas and New Mexico could suffer major blizzards, bringing up to 16in (41cm) of snow.
The storms across the South have been unusually powerful for winter.
Reports from Texas said churches were destroyed, cars mangled and trees toppled across a 64km (20 mile) zone from south of Dallas up to suburbs in the north-east.
Garland police believed that tornado-strength winds late on Saturday were the cause of car accidents, Melinda Urbina from the Dallas County Sheriff’s office, told the BBC.
Ms Urbina said the winds “tossed cars around” and vehicles were later found below Interstate 30, about 15 miles (24km) north-east of Dallas. She urged local residents to stay off the roads.
In a Sunday morning briefing, Lt Pedro Barineau, of Garland police, said 600 buildings had been damaged.
he Red Cross is setting up shelters for those with damaged homes.
Police said all street and highway lights had been knocked out, leaving officers working in the dark overnight.
Two people were found dead at a petrol station in Copeville, and a third was killed in Blue Ridge, reports in local media said.
Kevin Taylor, a church pastor in Glenn Heights, south of Dallas, described to WFAA how his church began collapsing around him.
“Doors began to turn inward, when I saw that I figured the glass was going to shatter and hit me in the face, so I broke and ran down the hallway and by the time I got just a few feet everything collapsed and went dark and fell on top of me,” he said, adding: “By the grace of God I’m here though.”
At least 30,000 people were reportedly without power, and there were reports of burst gas pipes.