SHAWNEE, Oklahoma (CNN) -- A rash of tornadoes destroyed homes and tossed trees around like toothpicks as it ripped through Oklahoma and the Midwest on Sunday and Monday.

And the destructive weather isn't over. Baseball-sized hail, wind gusts and tornadoes could pummel parts of the central Plains and Midwest through Monday.

"Today could be potentially as dangerous as yesterday," CNN meteorologist Indra Petersons said Monday morning, pointing to a wide swath of the country spanning from Texas to Michigan. "We're talking about 500,000 square miles under the gun for severe weather."

Early Monday morning, a tornado touched down in Golden City, Missouri, and tore through two counties, Barton County Emergency Management Director Tom Ryan said. The number of injuries and extent of damage were not immediately clear.

Oklahoma Gov. Mary Fallin declared a state of emergency after tornadoes tore through 16 counties in her state Sunday. Twenty-three people were injured, she told CNN.

One man was killed in Pottawatomie County, Oklahoma, where a twister reduced trailer park homes to piles of debris.

In the hardest-hit areas, the damage was devastating, said John Welsh, a helicopter pilot for CNN affiliate KFOR.

"Everything was just gone," he said. "Like you took the house, you put it in a gigantic blender, you turned it on pulse for a couple minutes and then you just dumped it out."

The storm left highways littered with debris, smashed cars and flipped over semi trucks. An 18-wheeler blew off an overpass on Interstate 40 and was practically flattened.

An estimated 300 homes were damaged or destroyed across the state, Red Cross spokesman Ken Garcia said.

Dozens of deputies sifted through the rubble at Steelman Estates trailer park overnight, Pottawatomie County Sheriff Mike Booth said. Two people reported missing there were found late Sunday night.

As many as 28 tornadoes were reported in Oklahoma, Kansas, Illinois and Iowa, according to the National Weather Service, with Oklahoma and Kansas the hardest hit. Some of those reports might have been of the same tornado.

A tornado that touched down near Wellston, Oklahoma, appeared to be a half-mile wide, according to KFOR.

"It's tearing up everything," the affiliate's helicopter pilot said. "Just ripping everything up in its sight."

Fallin said she planned to survey damage throughout the state Monday.

"We're still in the rescue and recovery stage, trying to get through the various communities," she said. "We had so many different tornadoes throughout the state, it was difficult to keep up with all that was going on because it was all happening within an hour to three-hour time span."

Eleven patients were being treated at St. Anthony Shawnee Hospital in Shawnee, Oklahoma, including one in critical condition, spokeswoman Carla Tollett said.

Ethan Mignard told CNN's iReport he caught a terrifying glimpse of a tornado as he rushed to take shelter at a school near the apartment where he lives.

"It was six miles away but it looked like it was right on top of you," Mignard said. "It was huge. It looked like it wasn't going to be good for somebody. When we saw it we stepped on the gas of the car and got to the basement of the school as fast as we could."

After the storm passed, he went to nearby Dale, Oklahoma, to survey damage there. The stark landscape looked like something he'd seen before only on TV, said Mignard, who works for a local newspaper.

Large, rectangular patches of dirt were all that remained where mobile homes once stood. Cinderblocks were scattered across the ground like children's toys. Twisted metal and pieces of insulation filled the trees. At the site of one home, all that remained were the front steps.

"It looks so out of place. ... To think that you would have taken these stairs to enter a home," he said, "but instead, you look around from up there and you see total destruction everywhere."

More tornadoes were spotted in Iowa, near Earlham, Huxley and east of Dallas Center, according to the National Weather Service.

The agency also confirmed a twister in the northwestern Illinois county of Carroll.

A combination of factors -- including strong winds and warm, moist air banging against dry air -- means severe weather could continue sweeping across a wide swath of the country for days, Petersons said.

"Keep in mind we have all the ingredients out there that we need," she said.

Several of the states pummeled by weekend tornadoes could see more trouble Monday. Here's a quick look at CNN meteorologist Melissa Le Fevre's forecast:

Oklahoma

The Sooner State could see more strong storms late Monday afternoon, and flooding could become a problem Monday night.

Kansas

Showers and thunderstorms threaten the state through Monday. Heavy rainfall in some parts may lead to flood watches and warnings.

Iowa

Showers and storms are expected to develop Monday afternoon, with large hail possible. Though the threat of tornadoes looks low, they can't be ruled out.

Missouri

Heavy rainfall could flood parts of Missouri. Afternoon storms could produce large hail, damaging wind gusts and possible tornadoes in areas such as St. Louis.

CNN's Nick Valencia reported from Shawnee, Oklahoma. CNN's Catherine E. Shoichet and Holly Yan reported from Atlanta. CNN's Jareen Imam, Dana Ford, AnneClaire Stapleton, Sean Morris, Jackie Castillo, Alexandra Steele and Chris Friedman contributed to this report.

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