Millions face tornado and storm warnings in the Midwest.

More than 77 million people from the Midwest to the Southern Plains were under tornado or severe-storm warnings after multiple apparent twisters caused extensive damage in Illinois and Indiana.

More than 77 million people from the Midwest to the Southern Plains were under tornado or severe-storm warnings on Wednesday. Multiple apparent twisters caused extensive damage in Illinois and Indiana. Northern Illinois carried the highest risk with a "moderate" tornado warning covering about 2 million people in areas south and east of Chicago, including Joliet, Peoria and Bloomington. A tornado emergency was declared in Knox County, Indiana, and the National Weather Service described the situation as life-threatening. Known details: - More than 77 million people were under some form of tornado or severe-storm warning across the Midwest and Southern Plains. - Northern Illinois had a "moderate" tornado warning for about 2 million people including Joliet, Peoria and Bloomington; a marginal risk extended toward Texas and Tennessee. - A tornado emergency was declared in Knox County, Indiana, which the National Weather Service described as life-threatening. - Severe storms brought strong winds, heavy rain and large hail in the Chicago region, and flood warnings were in place along rivers in Illinois and Indiana. - PowerOutage.us reported more than 12,000 customers without power in the Midwest and about 23,000 in the Great Lakes region. - NBC Chicago reported significant but so far unquantified damage to homes, other buildings and roads in northern Illinois and northwest Indiana. Summary: Officials reported that multiple apparent twisters caused extensive damage in Illinois and Indiana, and more than 77 million people were under tornado or severe-storm warnings. Power outages and flood warnings were reported across parts of the Midwest and Great Lakes. Assessments of the full extent of damage are ongoing. Undetermined at this time.