CEDAR RAPIDS, IOWA - Hospital patients in wheelchairs and on stretchers were evacuated in the middle of the night as the biggest flood Cedar Rapids has ever seen swamped more than 400 blocks Friday and all but cut off the supply of clean drinking water in the city of 120,000.

As many as 10,000 townspeople driven from their homes by the rain-swollen Cedar River took shelter at schools and hotels or moved in with relatives.

About 100 miles to the west, the Des Moines River threatened to spill over the levees into downtown Des Moines, prompting officials in Iowa's biggest city to urge people in low-lying areas to clear out by Friday evening. The river was expected to crest a couple of hours later.

"We are perilously close to topping the levees," said Bill Stowe, public works director in the Iowa capital, population 190,000. He added, "It's time to step out of harm's way."

The flooding was blamed for at least two deaths in Iowa: A driver was killed in an accident on a road under water, and a farmer who went out to check his property was swept away.

Since June 6, Iowa has gotten at least 8 inches of rain. That came after a wet spring that left the ground saturated. As of Friday, nine rivers were at or above historic flood levels. More thunderstorms are possible in the Cedar Rapids area over the weekend, but next week is expected to be sunny and dry.

In Cedar Rapids, the engorged river flowed freely through downtown. At least 438 city blocks were under water, and in some neighborhoods the water was 8 feet high. Hundreds of cars were submerged, with only their antennas poking up through the water. Plastic toys bobbed in front of homes.

For decades, Cedar Rapids escaped any major, widespread flooding, even during the Midwest deluge of 1993, and many people had grown confident that rising water would pose no danger to their city.

The Cedar River was expected to crest Friday night at nearly 32 feet, an astonishing 12 feet higher than the old record, set in 1929.

Flooding left 2 inches of water in the emergency room at Mercy Medical Center in Cedar Rapids on Thursday night, and water spilling into the lower levels threatened to knock out the hospital's emergency generator.

A total of 176 patients -- some of them frail, about 30 of them from a nursing home at the medical center -- were moved to other hospitals in an all-night operation that was not completed until daybreak.

Gov. Chet Culver declared 83 of the state's 99 counties disaster areas, a designation that helps speed aid and opens the way for loans and grants. The damage in Cedar Rapids alone was a preliminary $737 million, Fire Department spokesman Dave Koch said.

The drenching also has severely damaged the corn crop in America's No. 1 corn state and other parts of the Midwest at a time when corn prices are soaring and food shortages have led to violence in some poor countries. But officials said it was too soon to put a price tag on the damage.