The death toll in the southeast United States climbed to 25 on Sunday after less than a week of tumultuous weather ─ unusual warmth, tornadoes and torrential downpours ─ sparked flooding and caused damage that wreaked havoc during the Christmas holiday.

Millions of residents in the region are struggling to recover from fierce storms and heavy flooding.

With more severe weather expected across the central United States, forecasters are warning of airport delays and flooded roads as travelers return home after the Christmas holiday.

Feeding on unseasonably warm air, storms left a trail of destruction in rural communities from Alabama to Illinois.

"A variety of dangerous weather conditions will continue across the middle of the country through Sunday," the National Weather Service said.

It warned of "blizzard conditions" from west Texas into Kansas, and "hazardous ice accumulations" in Oklahoma. "Dangerous flooding will extend from north Texas to central Illinois," it said.

Flood warnings and advisories also remained in effect in parts of Mississippi, Tennessee, Alabama, Kentucky and other areas in the southeast.