Potent thunderstorms have been blamed for one death and have left more than 200,000 people without power across the southern US.
Fierce winds are also expected to wallop parts of several states as new storms form on Thursday, forecasters said.
Fallen trees ripped down power lines and crashed into buildings along a line from Texas to Alabama overnight and into Thursday morning, the national Storm Prediction Centre reported.
A few isolated tornadoes were reported.
Winds of up to 137km/h damaged roofs on Wednesday in the northeast Texas city of Greenville, the National Weather Service reported.
In Mississippi a 19-year-old man died when a tree fell on his home on Wednesday night.
More than 70,000 homes and businesses were without power in Arkansas on Thursday, and more than 30,000 outages each were reported in Texas, Louisiana and Alabama, where crews were working to remove toppled trees and clear blocked roads.
The storms were moving eastward, with more severe weather possible on Thursday in Alabama and Georgia and all the way up to Pennsylvania.
Thursday afternoon will also bring the risk of some tornadoes and very large hail to flood-weary residents of the Missouri River Valley.
In Ohio, heavy rains led to landslides and flooded highways.
Flood waters inundated commuter train stations and forced services to be suspended between Philadelphia and New Jersey.
The Delaware River was overflowing its banks in places, and people were being rescued from high water.
