A storm system sweeping over large areas of the U.S. South and Midwest resulted in at least 16 weather-related deaths by early Sunday, with overnight tornado and flash flood warnings setting up more severe weather that forecasters say could cause rising waterways for days to come.

At least 16 people are believed to have died after tornadoes, heavy rain and flash flooding battered parts of the South and Midwest in the United States. Among them was a 9-year-old boy, who was swept away while walking to a school bus stop in Kentucky on April 4.