At least seven people were killed and dozens were injured on Sunday as a destructive storm struck northeastern Iowa.

In Central Iowa, six people were killed and at least 50 houses destroyed by a powerful twister in the small towns of Parkersburg and New Hartford. The Des Moines Register reported that the tornado ripped off the roof of Parkersburg’s high school.

In Hugo, Minnesota, a two-year-old child died, and the tornado also devastated dozens of homes in nearby Minneapolis.

A tornado near Dunkerton - about 40 miles east of Parkersburg – flung debris, moving at 23 miles per hour.

Trees, power lines and houses were also damaged by marble-sized hail that fell in Waterloo.

On Saturday, two people were found dead in south-central Kansas in a car accident that was caused by a tornado, authorities said.

The storm system formed on the divide between warm air to the east and cool air to the west, creating the ideal conditions for tornadoes.

More than 100 people were killed in the United States by tornadoes so far this year. According to Reuters, Roger Edwards, a meteorologist at the Storm Prediction Centre in Norman, Oklahoma, said the death toll was very high this year, because, unfortunately, tornadoes hit population centers.

An average of about 54 people died in U.S. because of tornadoes each year between 1997 and 2006.