Emergency responders on Monday searched through wreckage in parts of Texas and Arkansas after a line of tornadoes battered several small communities, killing at least five people, including a young couple whose daughter survived.
Eight people were still missing, raising the possibility that the number of dead could climb.
The couple in their late 20s or early 30s died when a twister hit their mobile home late Sunday in the Arkansas town of Nashville, Howard County Coroner John Gray said.
Their daughter was 1 or 2 years old. He did not release the parents' names.
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Once the word spreads, he added, the deaths will be a blow to the community.
"That's what it's like in a small town," Gray said. "You either know them or you know somebody who knows them."
In neighbouring Texas, a likely tornado pummeled the small town of Van, damaging about 30 per cent of the community, according to Chuck Allen, fire marshal and emergency management coordinator for Van Zandt County.
Authorities confirmed at least two deaths as they surveyed the damage. Eight people were still unaccounted for in Van, population 2,600, about 112 kilometres southeast of Dallas.
Rescuers went door to door following the storms. Damage appeared to be widespread, with trees uprooted and numerous homes and buildings flattened or ripped apart.
About 50 people spent the night at an American Red Cross shelter at a church.
Firefighters in Corsicana, about 97 kilometres southwest of Van, recovered the body of a motorist early Monday after weekend storms dumped 28 centimetres of rain.
Preliminary reports indicate 20 to 25 tornadoes formed Sunday in South Dakota, Iowa, Oklahoma and Texas, according to meteorologist Greg Carbin of the Storm Prediction Center in Norman, Oklahoma.
The storm system was expected to slowly move east, he said, with a low possibility for tornadoes in lower Michigan on Monday. Thunderstorms were forecast from Texas to the Great Lakes region.
"This is certainly not an atypical system for spring where you've got the remnants of winter but the onset of summer," Carbin said.
The National Weather Service believes at least one tornado hit Van on Sunday night, senior meteorologist Eric Martello said. Weather service crews were surveying the area Monday.
Floods resulting from the same storm system that rolled across North Texas caused a huge sinkhole to open up in Granbury, some 64 kilometres southwest of Fort Worth. The 12-metre-wide sinkhole swallowed the parking lot of a supermarket and damaged water and sewer lines beneath, WFAA-TV reported.
Farther north, in Lake City, Iowa, a suspected tornado tore the roof from a high school as about 150 students, family and faculty attended an awards ceremony inside Sunday night.
Dave Birks, girls' basketball coach at South Central Calhoun High School, said people were able to flee to the basement and locker room area about two minutes before the twister arrived.
"The lights went off, and everyone's ears kind of popped," Birks said, adding that school windows were blown out and insulation was scattered nearby. He also said the high jump pit from the school's outdoor athletic complex was missing, and hurdles were scattered everywhere.
Much earlier Sunday, storms struck the small town of Delmont in South Dakota, hurting nine people.
"Our house is flat. There is nothing left," said Stephanie Lunder, 34, who took shelter with her husband and four children in the basement.
The town's 200-plus residents were asked to leave for safety reasons, state Department of Public Safety spokeswoman Kristi Turman said. They were to be allowed back on Monday to assess their property.
Elsewhere, winter seemed to return briefly to parts of the Dakotas.
The National Weather Service posted winter weather advisories and warnings for southeastern North Dakota and north-central South Dakota, with snow and strong winds expected. The same area experienced more than 20 centimetres of snow over the weekend, breaking snowfall records for those dates in Rapid City.
On Sunday, another likely tornado ripped roofs off buildings and damaged trees near Denton, about 64 kilometres northwest of Dallas. There were no reports of injuries or fatalities.
Torrential rains led to widespread flash flooding. Authorities in Denton County said two groups of people had to be taken by helicopter to safety.