The storms produced winds of more than 100 mph in some cases as they moved through Iowa and Illinois.
It’s unclear whether there were any injuries.
More than a million homes and businesses in the Midwest are without power, including a third of all of customers in Iowa.
The severe weather cleared out of Chicago by Monday evening and was stretching from Michigan and Indiana to southern Illinois and eastern Missouri, near St. Louis, CNN meteorologist Taylor Ward said, adding, “The threat will continue to push east, and the storms will slowly ease as we head later into the evening and overnight period.”
There were more than 300 severe wind reports — of gusts more than 58 mph — by Monday evening, starting in eastern Nebraska on Monday morning and going to Indiana by the evening, according to the Storm Prediction Center, Ward said.
The storms are part of what the National Weather Service’s Storm Prediction Center called a “particularly dangerous situation.”
Tornado warnings were in effect west and north of Chicago Monday afternoon.
“PDS severe thunderstorm watches are rare, and reserved for only the strongest thunderstorm events,” CNN meteorologist Brandon Miller said.
A wind gust of 106 mph in Marshall, Iowa, was reported as the storm passed through.
A derecho (pronounced similar to “deh-REY-cho”) is a widespread, long-lived wind storm associated with a band of rapidly moving showers or thunderstorms.
This storm complex is within the same area that is also under a moderate risk (level 4 of 5) for severe storms. The SPC upgraded this risk level Monday afternoon because of the formation of the derecho. The risk area included over 13 million people.
In addition to wind damage, tornadoes and large hail — one and a half inches in diameter — are possible.
CNN Senior Meteorologist Dave Hennen contributed to this report.