Rain-swollen rivers threatened more flooding on Thursday in Arkansas, Louisiana, Illinois and Oklahoma, as Tulsa's mayor warned that the decades-old levee system in his city would be at risk even as waters receded through the weekend.

Since early last week, a spate of deadly tornadoes has caused widespread damage across the central United States while torrential downpours unleashed record floods, turning highways into lakes and submerging all but the roofs of some homes.

The violent weather has been blamed for least 16 deaths across several states in the nation's midsection.