Washington  - The Mississippi River flood crest was headed downstream toward St. Louis, Missouri, on Wednesday, bursting at least two more levees, flooding another 12,000 hectares of farmland in Illinois and wiping out bridges along the way.

Thousands of volunteers hastened to reinforce flood dams with 13 million sandbags supplied by the US Army Corps of Engineers, which expects another 20 or 30 levees to break as the crest moves south.

Julie Shepard, of the Adams County Emergency Management, told CNN that the levees broke between 1 and 6 am Wednesday.

Only one human death has been reported during nearly a week of flooding of the nation's mammoth corn-growing region.

Among the animals killed in the flooding were two buffalo which drowned after being spooked by well-intentioned people trying to lure them to safety with hay, the Des Moines Register reported online.

"Two of them were spooked and jumped back in the river and drowned," Muscatine County farmer Louis Broders was quoted as saying.

A top engineer corps officer said in broadcast remarks that most of the levees are protecting agricultural land.

"It's only natural when you farm on a flood plain, you will have problems," he said.

US President George W Bush was to visit the flood region on Thursday - a scene reminiscent of the 2005 Hurricane Katrina disaster that his administration so badly mishandled.

A local US senator from Iowa, Charles Grassley, a fellow Republican, had some advice for Bush before his arrival.

"My advice to him is dont say, 'Youre doing a good job, Brownie'," Grassley was quoted as saying in the Register.

Bush delivered those words of praise to his federal emergency management administrator Michael Brown as tens of thousands of New Orleans residents were stranded by rising floodwaters without food or evacuation plans - images that provoked outrage around the country and the world.

Grassley said Bush will be spared the worst of the flood experience, which he called a "500-year-flood" at its peak. The waters have since receded in hard-hit Iowa as the water moved down the Mississippi.

Hes going to get there when its at a level of 100-year. Hes going to see a lot of damage," Grassley said.

Extensive damage to the region's major crop, corn, and other foodstuffs was estimated at 2.7 billion dollars, the Des Moines Register reported online.

The White House said Tuesday it was concerned about the fallout for grain and livestock prices, already under pressure from worldwide soaring demand for fuel and food.

The Mississippi drains much of the US Midwest from Minnesota to New Orleans. (dpa)