A potent storm that already plunged parts of California underwater has started to deal a serious blow to the eastern half of the US with flooding rain, severe thunderstorms, tornadoes, snow and ice all expected.

Millions of Americans are in the path of a storm that is hitting parts of Tennessee, Kentucky and Virginia the hardest, with rainfall reaching several inches.

Much of the eastern U.S. braced for a renewed round of harsh, soggy weather on Saturday. Kentucky, Tennessee, West Virginia and Arkansas were under flood warnings, and residents were warned by the National Weather Service to stay off roads.

Gov. Andy Beshear preemptively declared a state of emergency in Kentucky, where flash flooding was expected into Sunday.

A powerful storm moved through Kentucky and other parts of the South, creating a risk of flash flooding through Sunday morning.