GREENWOOD, Miss. — At least 31 people were killed and more than 200 injured after a violent tornado outbreak tore through the lower Mississippi Valley overnight Saturday into Sunday, leveling neighborhoods in Greenwood, Indianola and the western suburbs of Tuscaloosa, Ala., and stretching emergency-response systems already drawn down by months of war-related federal redeployments, state and local officials said.

Mississippi Gov. Tate Reeves declared a state of emergency in 14 counties before dawn Sunday and requested a presidential disaster declaration by mid-morning, and Alabama Gov. Kay Ivey followed with an emergency declaration covering nine counties in the state’s western tier. The National Weather Service confirmed at least four tornadoes of EF-3 strength or stronger, including a long-track wedge that traveled roughly 71 miles from south of Greenville, Miss., across the Delta and into Carroll County before dissipating near the Yazoo River.

“This is the worst outbreak we have seen in the Delta in a generation, and it came in the dark, which is the part that frightens forecasters most,” said Brad Bryant, the meteorologist in charge at the National Weather Service forecast office in Jackson, in a briefing to reporters Sunday morning. “We had the watches out. We had the warnings out. The atmosphere did exactly what we said it would do. The problem is that at two o’clock in the morning in a mobile-home park, a warning on a phone is only as good as a phone that is charged.”

The Storm Prediction Center in Norman, Okla., had issued a rare high-risk outlook for the lower Mississippi Valley on Saturday afternoon, warning of “strong, long-track tornadoes” after a powerful upper-level trough collided with a moisture-laden Gulf airmass that forecasters had been tracking since Thursday. The first tornado warnings of the night went out shortly before 11 p.m. local time over Washington County, Miss.; the last warning expired in west-central Alabama at 5:42 a.m. Sunday.

In Greenwood, where at least 11 people were confirmed killed, a quarter-mile-wide tornado crossed U.S. 82 and tore through the Pelican Bay neighborhood at roughly 1:15 a.m., flattening rows of single-story homes and a Baptist church that had been rebuilt only four years earlier. Mayor Carolyn McAdams, walking the debris field with a federal damage-assessment team Sunday morning, said the city’s small police and fire departments had been on the line continuously since midnight.

“We are looking, house by house, and we are not yet done looking,” McAdams said. “We will not have an accurate count until tonight. What I can tell you is that the people who answered the radios at two o’clock in the morning did not stop, and they are still not stopping.”

The outbreak hit a region where the federal disaster-response footprint has thinned visibly over the last six weeks. Three of the Federal Emergency Management Agency’s regional Incident Management Assistance Teams normally available for surge deployment in the Southeast had been reassigned through April to support consequence-management planning around the Iran war, two senior FEMA officials said in interviews Sunday, speaking on condition of anonymity because they were not authorized to discuss internal staffing. Two of those teams were recalled to civilian rotation only on Wednesday, the day the Iran-Israel ceasefire took effect, and were still in transit when the storms developed.

“We have what we need on the ground today, but we got there about eight hours later than we would have a year ago,” said one of the officials. “That is not a criticism of anyone. That is what happens when a country fights a war and a tornado in the same month.”

FEMA Administrator Deanne Criswell, who was in Atlanta on Sunday morning meeting with regional staff, said in a statement that federal urban search-and-rescue task forces from Tennessee and Texas had been activated overnight and were expected to be operational in Greenwood and Tuscaloosa by Sunday afternoon. The agency, she said, had also approved an immediate transfer of mobile housing units staged at a depot in Selma, Ala., for war-related contingency use into the Mississippi response.

In Tuscaloosa County, where the western suburbs of Northport and the unincorporated community of Coker were among the hardest hit, Sheriff Ron Abernathy said at a Sunday morning news conference that at least nine people had been killed and that two mobile-home parks along Highway 82 had been “effectively erased.” The county’s emergency operations center had logged 612 separate calls for service between midnight and 6 a.m., the sheriff said, a volume he described as “outside anything in our playbook.”

Public-health officials warned Sunday that the death toll was likely to climb as search teams reached structures collapsed onto basements and storm shelters, and that the medical impact of the outbreak would extend well beyond the immediate injuries. The University of Mississippi Medical Center in Jackson, which received 47 trauma transfers overnight, activated its mass-casualty protocol for the first time since 2021. Baptist Memorial Hospital-Golden Triangle in Columbus diverted non-emergency cases to surrounding facilities through Monday.

“After a storm like this, the second wave of casualties comes from the things that are not the storm,” said Dr. Thomas Dobbs, the former Mississippi state health officer who now directs the John D. Bower School of Population Health at UMMC. “Carbon monoxide poisoning from generators run inside garages. Cardiovascular events in older residents who are clearing debris in the heat. Tetanus from puncture wounds. Heat stroke when the power stays out for a week. We have between seventy-two and ninety-six hours to get ahead of that curve, and we know what to do.”

The American Red Cross opened 14 shelters across Mississippi, Alabama and west Tennessee by Sunday morning and said it expected to scale to 24 by Monday evening as displaced families moved out of damaged neighborhoods. Red Cross regional disaster officer Brad Kieserman, briefing reporters from Memphis, said the organization had moved 18 emergency-response vehicles into the affected zone overnight and was coordinating mental-health volunteers through state behavioral-health agencies.

“The first 48 hours, people are in motion and adrenaline carries them,” Kieserman said. “Around hour 60, the adrenaline runs out, and people sit down on what used to be their porch and they cannot stand back up. That is when our mental-health teams have to be in place. We have learned that the hard way.”

In Washington, President Donald Trump, who was at Mar-a-Lago for the weekend, posted Sunday morning that he had spoken with Reeves and Ivey and that federal assistance would be “fast and complete.” The White House said in a brief statement that the president had directed the Department of Homeland Security to expedite the disaster declaration process and had instructed FEMA to “draw on every available resource, including those returning from overseas contingency support, without delay.”

Climate scientists cautioned against drawing immediate conclusions about the role of warming in any single outbreak but noted that the geographic shift of severe-weather risk eastward out of the traditional Plains “tornado alley” and into the Mississippi and Tennessee valleys had become a robust signal in the research literature over the past decade. Dr. Victor Gensini, a professor of meteorology at Northern Illinois University who has tracked the trend, said in a phone interview that the Mid-South was now “the single highest-risk corridor in the country for nocturnal long-track tornadoes” and that the population exposed to that risk had grown faster than the response infrastructure around it.

“The hazard is moving where the people are, the people are in housing that does not perform well under wind load, and the storms are increasingly happening at night,” Gensini said. “Tonight was the version of that sentence that we have been writing in papers for ten years.”

The National Weather Service said another, smaller round of severe weather was possible across the Tennessee Valley and into the southern Appalachians on Sunday afternoon and evening, and forecasters in Birmingham, Memphis and Nashville urged residents to keep weather radios on and to have a sheltering plan in place before sunset. Federal and state officials said additional damage assessments, casualty figures and shelter capacity updates would be released Sunday evening.