Rescuers are scouring the rubble of mobile homes and houses in search of survivors of a powerful tornado that rampaged through south-east Alabama and killed at least 23 people.

The trail of destruction was at least half a mile wide and overwhelmed rural Lee County's coroners' office, forcing it to call in help from the state.

"The devastation is incredible," Lee County Sheriff Jay Jones said.

Drones flying overheard equipped with heat-seeking devices had scanned the area for survivors, but dangerous conditions halted the search late on Sunday, Mr Jones said.

The tornado was part of a powerful storm system that also slashed its way across parts of Georgia, South Carolina and Florida.

Mr Jones said the twister travelled straight down a county road in the rural community of Beauregard, reducing homes to slabs.

The National Weather Service confirmed late on Sunday that a tornado with at least an F3 rating caused the destruction in Alabama.

Although the statement did not give exact wind estimates, F3 storms typically are gauged at wind speeds of 158mph to 206mph.

After nightfall on Sunday, the rain had stopped and pieces of metal debris and tree branches littered roadways in Beauregard. Two sheriff's vehicles blocked reporters and others from reaching the worst-hit area. Power appeared to be out in many places.

President Donald Trump tweeted: "To the great people of Alabama and surrounding areas: Please be careful and safe. Tornadoes and storms were truly violent and more could be coming. To the families and friends of the victims, and to the injured, God bless you all!"

Rita Smith, spokeswoman for the Lee County Emergency Management Agency, said about 150 first responders had quickly jumped in to help search the debris after the storm struck in Beauregard.

At least one trained dog could be seen with search crews as numerous ambulances and emergency vehicles, lights flashing, converged on the area.

No deaths had been reported by Sunday evening from storm-damaged Alabama counties other than Lee County, said Gregory Robinson, spokesman for the Alabama Emergency Management Agency, but he said crews were still surveying damage in several counties in the south-west of the state.

Numerous tornado warnings were posted across parts of Alabama, Georgia, Florida and South Carolina on Sunday afternoon as the storm system raced across the region.

Weather officials said they confirmed other tornadoes around the region by radar and would send teams out to assess those and other storms.

In rural Talbotton, Georgia, about 80 miles south of Atlanta, a handful of people were injured by either powerful straight-line winds or a tornado that destroyed several mobile homes and damaged other buildings, said Leigh Ann Erenheim, director of the Talbot County Emergency Management Agency.

News footage showed smashed buildings with rooftops blown away, cars overturned and debris everywhere. Trees all around had been snapped bare of branches.