The surging Mississippi River spilled over levees in two towns in the state of Illinois and is threatening to deluge other parts of the central United States.

The Army Corps of Engineers says 20 levees in the central U.S. have already overflowed - and up to 30 more are in danger of overflowing.

Central U.S. river towns are at risk as floodwaters that submerged parts of two of the state of Iowa's largest cities are now flowing downstream.  

Residents have joined members of the National Guard in a desperate effort to strengthen levees with sandbags.

Meanwhile, Iowa is cleaning up after widespread flooding inundated homes, destroyed crops and cut off highways and bridges.

At the White House Tuesday, U.S. President George Bush expressed concern for the flood victims.  He is to visit Iowa Thursday to inspect the damage.

Some information for this report was provided by AP and Reuters.