In Central Iowa, the small towns of Parkersburg and neighboring New Hartford suffered direct hits in the late afternoon from at least one powerful twister, killing six people and leaving a trail of 50 to 60 splintered or flattened homes and other structures.
Rescue teams armed with listening devices and expertise in digging through debris were searching in Parkersburg, a town of 1,800 roughly 80 miles northeast of Des Moines, said Bret Voorhees of Iowa's emergency management. Another 650 people live in New Hartford.
A two-year-old child died in Hugo, Minnesota, near Minneapolis, where dozens of homes were destroyed by what was likely a tornado, according to local media reports.
The storms fired up Sunday afternoon and brought hail and high winds on a frontal boundary from Texas to Minnesota.
The slow-moving storm system formed on the divide between warm air to the east and cool air to the west, creating ideal conditions for tornadoes. Tornado season in the United States peaks in spring and early summer but twisters also pose a threat in the fall.
Added to the two people killed on Saturday in Kansas when their car was swept up and tossed by a tornado generated by the same storm system, there have been more than 100 people killed in the United States by tornadoes so far this year.
"We've definitely had an unusually high death toll, which is the misfortune of having tornadoes hitting population centers," said Roger Edwards, a meteorologist at the Storm Prediction Center in Norman, Oklahoma.
Tornadoes are blamed for an average of 54 U.S. deaths a year between 1997 and 2006.
The Storm Prediction Center, which tracks and issues warnings for the "Tornado Alley" between Texas to the Upper Midwest, said there have been reports of roughly 1,000 tornadoes this season compared to 500 or 600 by this time in an average year. There may not have been that many tornadoes, though, as there can be multiple reports for a single twister.
This particular storm system produced tornadoes three consecutive days as it gradually moved east, though its intensity was expected to wane, Edwards said.
(Reporting by Carey Gillam in Minneapolis, Andrew Stern in Chicago, editing by Todd Eastham)