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.

Tornadoes and violent winds flattened homes and ripped apart buildings from Oklahoma to Indiana in the first round of storms that are expected to bring record-setting rains and life-threatening flash floods across the nation's midsection in the coming days.

A once-in-a generation extreme weather event is beginning Wednesday with a tornado outbreak and will continue into the weekend with dangerous, life-threatening flooding.