Deadly tornadoes have roared through Alabama, toppling trees, demolishing homes and knocking out power to thousands of people.

The storms were part of a broad swathe of violent weather sweeping across the US Deep South. At least five fatalities and an unknown number of injuries were reported.

Authorities posted video and photos showing large trees blocking roads and damaged utility poles leaning menacingly over streets littered with debris from badly damaged homes. More than 20,000 customers were without power in Alabama.

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Search and rescue efforts were complicated as strong weather continued to rake across the region.

“We have been told to be prepared for another round of storms,” said Major Clay Hammac of the Shelby County sheriff’s department.

Forecasters warned of dangerous thunderstorms, flash floods and possible twisters from eastern Mississippi into western Georgia, and northward into Tennessee and Kentucky.

The National Weather Service office in Birmingham, Alabama, has issued a “tornado emergency” for the area, indicating there is a tornado that could have a potentially significant impact to human life and catastrophic destruction to property.

Tweet from @NWSBirmingham

Up to 100mm of rain – with higher amounts possible – is expected in northern Alabama, according to the National Weather Service in Huntsville.

-with AAP