Violent tornadoes ripped through parts of the U.S., wiping out schools and toppling semitractor-trailers in several states, part of a monster storm that killed at least 18 people as more severe weather was expected late Saturday.

At least 12 fatalities have been reported in Missouri, according to the Missouri State Emergency Management Agency. The deaths come as a massive storm system moving across the country unleashed winds that damaged buildings, whipped up deadly dust storms and fanned more than 100 wildfires.