(USA Today) -- Severe storms roared through the Plains and Midwest on Sunday, spawning tornadoes that damaged buildings, ripped off roofs and tossed big trucks like toys in Oklahoma. At least 21 people were injured across the state, the Associated Press reported.
Another tornado kicked up debris in Wichita, Kan., and a tornado was reported near Des Moines, Iowa, on a day when there were multiple twisters reported across a broad central section of the country.
Keli Cain, a spokeswoman for the Oklahoma Department of Emergency Management, told the Associated Press that 21 people were injured across Oklahoma, not including those who suffered bumps and bruises and chose not to visit a hospital.
A person answering the phone at the Shawnee-Pottawatomie County emergency management office, who declined to give his name, said he had no damage reports or information on injuries.
Interstate 40 was closed by the Oklahoma Highway Patrol after winds overturned semi-tractor trailer trucks and other vehicles, Newsok.com reported.
The Associated Press said several mobile homes in the Shawnee area were leveled.
KFOR-TV showed footage of homes damaged and cars and trucks flipped from highways near Shawnee, Okla. Other video showed flashes from electrical transformers blowing out as they were hit by high winds or debris from the tornado near Edmond.
Sedgwick County, Kan., emergency management director Randy Duncan says officials are grateful for few reports of damage from a tornado that touched down near Wichita Mid-Continent Airport. He told CNN the area emerged "relatively unscathed.''
Tornado watches were posted from Oklahoma to southern Minnesota. Forecasters had been warning for days that severe storms were likely across the region.
"I knew it was coming," said Randy Grau, who huddled with his wife and two young boys in their Edmond's home when the tornado hit. He said he peered out his window as the weather worsened and believed he saw a flock of birds heading down the street. "Then I realized it was swirling debris.''
In Iowa, a tornado touched down about 30 miles west of Des Moines near the town of Earlham, the Des Moines Register reported. It was moving northeast at 55 mph toward Adel, according to the National Weather Service.
The National Weather Service said it was tracking a confirmed tornado near Edmond, Okla., moving east at 30 mph around 4:19 p.m. CT.
The National Weather Service described the Oklahoma City area tornado as "large, violent and extremely dangerous.''
A helicopter pilot following the storm captured footage of an apparent funnel cloud near Wellston, Okla.
The Storm Prediction Center in Norman, Okla., said there is a risk of strong tornadoes in central parts of the state Sunday.
Forecasters say the storms - which could also bring large hail and damaging winds - are expected to form Sunday afternoon and that the advised area also includes portions of Kansas, Missouri and Nebraska.
In central Iowa, Sunday and the beginning of the week are "the biggest chance we've had for severe weather since 2011," forecasters at the National Weather Service told the Des Moines Register.
Meteorologist Kurt Kotenberg said a large low-pressure system is parking itself over the middle of the country and "really isn't going to move much over the course of the next few days. ... It's basically going to keep pulling up that nice Gulf (of Mexico) moisture that keeps fueling everything."
Overall, Iowa has a roughly 70% chance of severe thunderstorms from late Sunday afternoon through midnight, with more storms likely on Monday and Tuesday, Kotenberg said. The weather service's "hazardous weather outlook" warns of the potential for "all modes of severe weather possible," including golf-ball sized hail and winds in excess of 60 mph.
Kotenberg said tornadoes are most likely to the south - in Missouri, Kansas and Oklahoma - but within Iowa, Des Moines and points southeast could be at the greatest risk of seeing a twister in the state.
The threat of twisters comes less than a week after tornadoes left six dead, dozens injured and hundreds of homes destroyed in Texas and just shy of the two-year anniversary of the Joplin, Mo., twister that left 160 dead on May 22, 2011.
Contributing: The Des Moines Register; The Associated Press