(CNN) -- Record-breaking flooding along the Missouri River is putting levees and residents to the test, including an Iowa city that hopes an emergency embankment will do the job if a nearby levee fails.
"Everybody in the western part of the county is packing their stuff and going to higher ground," said Fremont County emergency management coordinator Mike Crecelius.
Water will rush from the Missouri River to the southern end of the city of Hamburg if the levee fails, as predicted, Crecelius told CNN Tuesday.
The U.S. Army Corps of Engineers reported a partial breach occurred Sunday morning at the levee in Atchison County, Missouri, near Hamburg.
The Iowa National Guard helped fortify the levee with sandbags. Some water has already flooded farmland in Fremont.
"Putting sandbags will temporarily delay" levee failure, said Corps spokeswoman Monique Farmer.
Crews are building up a wall or berm on the edge of town, with the aim of having it heightened and strengthened by next week.
Several hundred residents in Hamburg, a town of about 1,200, have been evacuated, Crecelius said.
Some portions of western Fremont County could see 2 to 10 feet of water if the Missouri rushes over the banks, he said.
"Once the river gets out there is no way to get the water back in," he said.
The levee breach followed weeks of high flows and record releases from dams in Montana and the Dakotas, according to the Corps.
Heavy rains and snow pack runoff could result in near-record flooding along parts of the Missouri River this year.
Five dams in North and South Dakota by mid-June will see peak releases of 150,000 cubic feet per second, Farmer said. That flow could continue into August, officials said.
The peak level was reached Tuesday at Oahe Dam, near Pierre, South Dakota. Video showed a massive amount of water gushing through the dam.
This year's flooding is putting levees to the test along 1,700 miles of the Missouri. Temporary levees are being built in several locations.
Carlos Lazo, public affairs specialist with the U.S. Army Corps of Engineers, said 6.8 miles of emergency levees are being constructed at Pierre and Fort Pierre, across the river from each other.