HAMBURG, Iowa (AP) -- The swollen Missouri River is threatening to inundate a small southwest Iowa town where officials are piling massive sandbags on a faltering levee to contain floodwaters that could leave the community under several feet of water.
If efforts to protect the town - including building a secondary barrier - fail, part of Hamburg could be under as much as 8 feet of water for a month or more, Fire Chief Dan Sturm said. Flooding along the river this summer, expected to break decades-old records, will test the system of levees, dams and flood walls like never before.
"We're working against the clock," Sturm said as many residents packed up their homes and headed out of town. "There's a chance we can save ourselves from the worst of it. We just need some time. But if water gets in here, it's going to be here for a while."
The earthen levee that guards an area of farmland and small towns between Omaha, Neb., and Kansas City has been partially breached in at least two places south of the Iowa-Missouri border. And emergency management officials expect new breaches in the coming days as the river rises.
That means Hamburg could be only the first of many communities to get hit.
The last time the Missouri River crested at levels predicted for this summer was in 1952, before most of the major dams along the river were built. And the flooding is expected to last into mid-August.
The U.S. Army Corps of Engineers will be releasing more water than it ever has from the dams by mid-June, meaning there likely will be other levee problems like the ones near Hamburg, said Kevin Grode with the corps' water management office.
"With these high flows, there's the possibility of more levee breaches," Grode said.
Officials also predict the water will get high enough to flow over at least 11 levees in the area near Hamburg in the corners of southeast Nebraska, southwest Iowa and northwest Missouri.
The Army Corps began building a secondary flood wall to protect low-lying areas of Hamburg because it expects the northernmost breach of the floodwall, which is 5 miles southwest of town, to fully give way at some point.
That breach constituted a 10- to 15-foot-wide section of the levee collapsing in on itself on Sunday, said Kim Thomas, the head of the corps' emergency management office in Omaha, Neb. The corps evacuated its personnel from the area, and the Iowa National Guard used a helicopter to drop 22 half-ton sandbags on the weakened section, stabilizing it temporarily.
Although Hamburg is upriver, a full breach of that section of levee would cause floodwater to flow northward over the flat terrain and threaten the town's low-lying southern neighborhoods.
About half of Hamburg's roughly 1,100 residents were ordered Sunday to leave their homes within 24 hours, and that process was expected to be completed by Monday evening, said John Benson, a spokesman for Iowa's department of Homeland Security and Emergency Management.
Just across the state line in Missouri, several residents of Atchison County were also ordered to leave.
In a worst-case scenario, corps projections show that the volume of water released upstream during a levee break could leave 8 feet to 10 feet of standing water in the southern part of Hamburg. The area includes manufacturing and agricultural businesses. Water could reach the fire station and City Hall, but it likely wouldn't reach the northern part of town where most residents live.
Sturm said such a scenario "would be a calamity" for the town and officials are trying to contain as much water as possible.
"We're going to hope for the best and see what happens," Sturm said. "I don't want to admit defeat until I see that water coming into town."
Large sections of town sat empty Monday as crews scrambled to erect the western levee against the Missouri River. Local officials patrolled a levee along the Nishna River to the east, fearful that another few inches of rain would cause it to break and inundate the town.
Several residents voiced anger at the corps for not starting the water release sooner to spread it out over time.
"Talk about dropping the ball," said Terry Rutledge, who owns a car dealership and strip club in town. "They should have started making a move on this a long time ago, and they didn't. They've really blown it."
Rutledge and several employees piled couches, chairs, air compressors and a refrigerator onto a truck to move to his home in nearby Nebraska City. Rutledge said he has invited more than a dozen residents to stay with him if necessary.
Corps officials said they understood residents' frustrations. Omaha district commander Col. Bob Ruch said the corps was following its policies and trying to protect lives and minimize damage. He said the corps has been working to raise the levee near Hamburg an additional 5 feet to help protect the town.
Officials are also concerned about a section of a levee on the river's western banks, near Brownville, Neb., and crews are trying to determine the extent of possible damage there, the corps said.
The river is expected to crest at least 5 feet above flood stage in most of Nebraska, Iowa and Missouri, but the water level could be higher if more rain falls.
Associated Press writers Josh Funk in Omaha, Neb., and Chris Blank in Jefferson City, Mo., contributed to this report