In this aerial photo, homes are surrounded by floodwater, Wednesday, Dec. 30, 2015, in Pacific, Mo.

Missouri and Illinois were bracing for more flooding on Thursday as rain-swollen rivers, some at record heights, overflowed their banks, washing out hundreds of structures and leaving thousands of people displaced from their homes.

Days of downpours from a winter storm that spawned deadly tornadoes in Texas and significant snowfall in New England has pushed rivers in the U.S. Midwest to levels not seen in decades, the National Weather Service and local officials aid.

At least 24 people have died, mostly from driving into flooded areas in Missouri, Illinois, Arkansas and Oklahoma after storms dropped up to 12 inches (30 cm) of rain, officials said.

Flooding has destroyed hundreds of homes and businesses, and overflowing rivers could menace Southern states as the water moves downstream toward the Gulf of Mexico, the National Weather Service said.

“Floodwaters will move downstream over the next couple of weeks, with significant river flooding expected for the lower Mississippi into mid-January,” the NWS said.

Water rose to the rooftops of some structures in Missouri towns. Governor Jay Nixon spoke with President Barack Obama on Wednesday and received a pledge of federal support.

Two rivers west of St. Louis crested at historic levels, flooding local towns, disabling sewer plants and forcing hundreds of residents from their homes.

Some evacuees stayed with family or friends or went to hotels, while others found refuge in Red Cross shelters set up in the area.

The Mississippi River, the third longest river in North America, is expected to crest in the next few days in Thebes, Illinois, at 47.5 feet, more than 46 cm above the 1995 record, the National Weather Service said.

Several levees, including one along the Meramec River near St. Louis, were at risk of a breach, the St. Louis Post-Dispatch said.

Periods of below-freezing air in coming days will cause some flooded areas in Missouri and Illinois to turn icy, adding to the clean-up challenges, the forecasting site AccuWeather reported.

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