“At this time, we have 14 confirmed fatalities,” Lee County Sheriff Jay Jones said in a video posted on Facebook by a journalist from a local CBS affiliate.
Other people have been hospitalised, some with “very serious injuries”, while the search was still ongoing for more who are missing, he said.
Lee County coroner Bill Harris confirmed the death toll: “We’ve got 14 people dead at this time and I expect that number to go higher,” he told MSNBC.
“There are some children involved,” Harris said.
The National Weather Service (NWS office in Birmingham, Alabama tweeted that it could confirm at least eight deaths in Lee County and added that the toll was likely to rise, saying that there were “many injured & still missing”.
Jones described the damage caused by the storm as “catastrophic, based on the destruction of homes that we’ve seen”. The swath of destruction left by the storm was a quarter mile (0.4 kilometres wide and stretched for the “several miles that it travelled on the ground”, according to Jones.
Still and video images showed trees that had been snapped in two, debris-strewn roads and wrecked houses in the wake of the storm.
More than 5,000 people were left without power in Lee County, according to electricity outage tracker PowerOutage.US.
The NWS had issued a tornado warning for areas including Lee County earlier on Sunday, calling on residents to: “TAKE COVER NOW! Move to a basement or an interior room on the lowest floor of a sturdy building. Avoid windows.”
NWS Birmingham tweeted the “all clear” several hours later and urged people to “stay out of damaged areas so first responders can do their job.”
While Jones referred to a single storm, CNN reported that two tornadoes had hit Lee County in quick succession.
NWS Birmingham appeared to confirm that there were multiple twisters in the area, tweeting that the “first tornado to impact Lee County today was at least an EF-3 & at least 1/2 mi wide”.
The EF-3 designation — on a scale of 0 to 5 — means the tornado had winds of 136 to 165 miles (218 to 266 kilometres per hour.