Winfield, Missouri - The Mississippi River on Friday burst through an earthen levee that may have been weakened by burrowing muskrats, swamping a Missouri town and adding to billion-dollar losses in U.S. Midwest flooding that has fueled fears of soaring world food prices.

    The levee break, the 36th in the last two weeks, sent a torrent of muddy water into Winfield, a town of about 800 people north of St. Louis, where officials said about 3,000 acres of crop land was submerged.

    In all about 40,000 acres of land has now been flooded in Missouri.

    Fears that as many as 5 million acres of corn and soybeans have been lost to flooding in the world's largest grain and food exporter have pushed corn and livestock prices to record highs in the last week.

    The Midwest storms and torrential rains have killed at least 24 people since late May. More than 38,000 people have been driven from their homes, mostly in Iowa where 83 of 99 counties have been declared disaster areas.

    Missouri Gov. Matt Blunt said up to 150 homes may be flooded in Winfield, where volunteers had labored for a week fortifying levees and piling sandbags. They began again at a fall-back position on Friday to prevent more widespread damage.

    "They really are involved in a race against that water," Blunt told reporters. "It's really just a reminder of how powerful a force the Mississippi River is."

    Animal Burrows

    Officials said the levee break began in an area where muskrats, semi-aquatic rodents common in U.S. lakes and streams, had been digging.

    "We believe the original breach was attributed to animal burrows created sometime in the past" and even though the holes were plugged, "the area remained problematic," the Lincoln County Emergency Operations Command said in a statement.

    Scattered heavy rains again were reported in the region on Friday and forecasters warned more flooding was a threat because the sodden ground can absorb little more.

    But the National Weather Service forecasts for Saturday and Sunday called for rains to ease off in the worst-hit areas.

    Heavy rains this month have caused more than $6 billion in crop damage in Iowa, Illinois, Indiana, Missouri and Nebraska, a key growing region of the world's biggest grain and feed exporter, according to the American Farm Bureau Federation.

    "It's a tragic, devastating disaster," Russ Kremer, a grain and livestock farmer who is president of the Missouri Farmers Union, said of the worst Midwest floods in 15 years.

    He said towns like Winfield and hundreds of thousands of acres of prime crop land submerged in the region represent "a complete loss for a lot of people. It will have a significant effect on the market."

    Corn prices hit a record at the Chicago Board of Trade in overnight screen trading on Friday at $8.25 per bushel in the July 2009 contract, more than double the 40-year average.

    Corn is the main feed for livestock, is used for ethanol fuel and contributes to hundreds of other food and industrial products throughout the economy.

    Before the floods, stockpiles of corn in the United States -- which ships 54 percent of all world corn exports -- had already been projected to fall to 13-year lows next year.

    So the effect on global food prices as U.S. prices rise has alarmed everyone from central bankers to food aid groups.

    Farmers Losing Hope

    Iowa Gov. Chet Culver said on Friday that 45,000 square miles of the state had been hit by tornadoes or flooding, including 340 towns, with extensive damage to road and rail lines at a cost reaching into the "tens of billions of dollars."

    "We are beginning a (recovery) effort which could take years," Culver said told reporters.

    Iowa officials said this week at least 2.5 million acres of corn and soybeans, well above 10 percent of planted acreage in the top U.S. producing state for those crops, needs to be replanted. But it is too late in the season for good yields on replanted fields.

    Jason Roose, an Iowa corn and soybean farmer who is an analyst for U.S. Commodities in Des Moines, said he had planned to replant his acreage this week.

    "But it didn't happen. I'm not able to do anything, and everyone else around here is in the same boat," he said.

    The Des Moines Register reported that the first half of 2008 was the wettest in Iowa since record-keeping began in the 19th century, with nearly 2 feet (0.7 meter) of rain.

    In Cedar Rapids, Iowa, where 4,000 homes were flooded two weeks ago, the city's broken sewage treatment plant was reported allowing 25 million gallons of raw sewage to drain into the Cedar River daily.

    Chemicals from farm fields and other toxic substances left behind as waters recede have created a potential health threat. But drinking water supplies remain unpolluted in most areas.

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    (Additional reporting by Lisa Shumaker and Sam Nelson in Chicago. Writing by Michael Conlon in Chicago; Editing by Peter Bohan and Xavier Briand).