Storms are tearing across the midwest in an outbreak of violent weather that forecasters predict could be "life-threatening."
By late Saturday, Nebraska was hit with baseball-sized hail, and dozens of tornadoes were reported across Iowa, Kansas, Oklahoma and Nebraska.
Rod Stuhr, a volunteer firefighter in Petersburg, Neb., said giant hail pounded the streets and "bounced about five to six feet up in the air," shattering the windows of homes and cars in in the area.
And Sheryl Machacek, the 911 director with the sheriff's office in Boone County, Neb., said the hail caused some damage but no injuries in and around Petersburg.
"After the storm went through, we had reports of windows out in homes and vehicles, citing damage and three and half inches of rain," she said.
The storms are only just beginning, according to Bill Bunting of the National Oceanic and Atmoshperic Administration's storm prediction center. "The tendency may be to see what's happening visually before you take action, but that may not be a luxury we'll have tonight."
After tornado sirens went off in Kansas, Angela Brown said people swarmed the Best Western she manages in Greenburg.
"They are just coming off the highway to shelter in the basement," she said.
Oklahoma and Kansas are expected to be the hardest hit, according to a rare high risk warning issued Friday by the National Oceanic and Atmospheric Administration's Storm Prediction Center on Friday.
Paul Walker, an Accuweather senior meteorologist, told ABC News that a warning two days in advance of a storm was unusual and cautioned that the weekend "should be particularly dangerous." Oklahoma had its first brush with the severe weekend weather on Friday when at least one tornado ripped through the town of Norman, where the University of Oklahoma is located, leaving 19 people hurt with "bumps and bruises" and a trail of property damage.
One patient was hospitalized and in fair condition Friday, said Norman Regional Hospital spokeswoman Kelly Wells.
Residents began assessing the damage today before preparing for another day of wild weather. A brick storefront was decimated by the storm. One woman told ABC News she lost the roof on her house.
"Fortunately, the portion of the roof that's left is right over our bedroom. I mean, it was there and gone before we could even get out of bed," she said.
The National Weather Service is urging residents in the danger zone to heed its strongly-worded warning.
"We're quite sure [Saturday] will be a very busy and dangerous day in terms of large tornadoes in parts of the central and southern plains," National Weather Service spokesperson Chris Vaccaro told the Associated Press. "The ingredients are coming together."
The storm system was moving toward the Rockies and energizing a warm, moist flow of air from the Gulf of Mexico, according to Accuweather.
Those conditions, plus differing wind directions in the atmosphere and on the surface, increased the likelihood of tornado-spawning storms today, Accuweather senior meteorologist Paul Walker said.
"All the pieces of the pie are coming together to make a particularly dangerous situation," he said.
California also dealt with severe weather on Friday when thunderstorms, hail and fierce winds pummeled parts of the state.
ABC News Radio contributed to this report.