"We have been hit. We are triaging and moving patients," a spokeswoman at Greater Regional Medical Center in the south-central Iowa city of Creston told CNN.
Conditions were favorable for violent and possibly long-lived tornadoes obscured by rain and darkness throughout central and eastern Kansas, Nebraska and Oklahoma, the National Weather Service said.
"If you're on the road, get off as soon as you can and find some shelter," Kansas Gov. Sam Brownback said in an advisory.
Hailstones the size of tennis balls were reported in Nebraska as a cold storm front moving east was fueled by a flow of warmer, moister air flowing up from the Gulf of Mexico. Similar conditions created tornadoes in Oklahoma Friday and sent rain rolling across Missouri and central Illinois early Saturday.
Another eastbound storm blew ashore in California Friday and was dropping snow in Arizona and New Mexico before rendezvousing with the gulf air over the wide-open Plains.
Southern California remained wet and chilly early Saturday after seeing wind, hail, plenty of spring showers and snow down to 4,000-foot elevations.
The Los Angeles Times said the snow was heavy enough to close the Grapevine on Interstate 5 north of the city and cause a spike in the number of accidents on the region's busy highways.