Rain-swollen rivers in the US Midwest forced the evacuation of hundreds of residents, threatened crops and livestock and left scores of buildings underwater on Wednesday after days of extreme weather in which 24 people died.

Several major rivers, including the Mississippi, were expected to crest at or above record levels as flood waters rushed toward the Gulf of Mexico, the National Weather Service said.

Flooding has closed many roads and parts of Interstate 44, a major artery running from west Texas to St. Louis.

Water rose to the rooftops of homes and businesses in Missouri, where Governor Jay Nixon called the flooding "historic and dangerous."

About 300 people in Valley Park, Missouri, west of St. Louis, were evacuated because a levee that protects the community might be breached by the Meramec River, said Chief Rick Wilken of the Valley Park Fire District.

"We have seven people who are going to wait it out," Wilken said. "Some people just want to hang onto their homes."

The American Red Cross had seven shelters open in St. Louis on Wednesday, and spokesman Zach Collins said people were trying to help each other. "There was one lady who only had $67 in her bank account but gave 34 of it for cereal and pop tarts and that sort of thing, just to give back," Collins said.

Louisiana Governor Bobby Jindal declared a state of emergency as the waters moved south toward his state. Flash flood warnings were issued for parts of the Carolinas and Georgia.

At least 24 people have died in Missouri, Illinois, Arkansas and Oklahoma in flooding after days of downpours that brought as much as 12 inches (30 cm) of rain to some areas. Most of the deaths resulted from people driving into flooded areas.

In Eureka, Missouri, along the Meramec River, Mayor Kevin Coffey said a man was rescued from atop the cab of his pick-up truck after spending the night in a parking lot to watch over his gun shop business.

"This is 4 feet (1.2 meters) above the worst flood we ever had," Coffey said after helping to put sandbags around a school. "The town looks like one huge lake."

Historic floods on the Mississippi in 1993, 1995 and 2011 occurred during warm weather, after snow melts in the north. AccuWeather senior meteorologist Alex Sosnowski called it highly unusual to have heavy flooding in winter and said it could presage trouble for the spring.

"The gun may be loaded again for another major flooding event," said Sosnowski, who cited the El Nino weather pattern as the source of recent heavy rains. "You're not supposed to get this kind of heavy rainfall during the wintertime."

Agriculture experts said that water standing more than a week could kill the soft red winter wheat crop. Export premiums for corn and soybeans were at their highest levels in weeks because of stalled barge traffic on swollen rivers.

Livestock also has been hard hit. About 2,500 hogs drowned in an Illinois barn after a creek overflowed its banks, said Jennifer Tirey, a spokeswoman for the state's Pork Producers Association.

"There was no electricity and roads were impassable. It was just impossible to get to those pigs," she said.

The US flooding is occurring at the same time as historic El Nino-related flooding across northern England. The El Nino weather phenomenon tends to disturb global weather patterns as ocean water temperatures rise above normal across the central and eastern Pacific, near the equator.

Several major rivers, including the Mississippi, and tributaries in Missouri and Illinois were poised to crest at record or above-record levels, the National Weather Service said, but parts of the region were already inundated.

Flood warnings were issued from eastern Oklahoma into southeastern Kansas, southern Missouri, central Illinois and parts of Arkansas, Kentucky, Tennessee, and the Florida panhandle.

While the rains have stopped for now, freezing weather is setting in, which will make the cleanup a miserable undertaking, Sosnowski said.

At the confluence of the Mississippi and Missouri rivers, about 20 miles (32 km) north of St. Louis, residents of the towns West Alton and Arnold were told to evacuate on Tuesday. About 400 residents and businesses in the town of Pacific also have evacuated.

The US Coast Guard closed a 5-mile (8 km) stretch of the Mississippi near St. Louis on Tuesday to all vessel traffic due to hazardous conditions.

The Mississippi River, the third longest river in North America, is expected to crest over the weekend at Thebes, Illinois, at 47.5 feet, more than a foot and a half (46 cm) above the 1995 record, according to the National Weather Service.

The severe weather has stranded tens of thousands of people during one of the busiest travel times of the year. More than 750 flights were canceled and 4,760 delayed as of mid-afternoon on Wednesday, according to FlightAware.com.