Six hundred residents in southwest Iowa were ordered Sunday to evacuate their homes after the Missouri River breached a levee across the border in Missouri.

The evacuation covers nearly half of the town of Hamburg, said Stefanie Bond, spokeswoman for the Iowa Department of Homeland Security and Emergency Management. Residents, most of them on the south side of the city of 1,141, were being told to get out within 24 hours.

The U.S. Army Corps of Engineers reported a levee was breached Sunday morning south of Hamburg in Missouri's Atchison County. The corps' Col. Robert Ruch said crews had been working Saturday on another issue near the breach and all workers were evacuated.

Gen. Derek Hill, head of the Iowa Department of Homeland Security and Emergency Management, characterized the breach as a "boil" — a leak that "shoots out like a small geyser" — that was 1 inch to 1½ inches in diameter.

Iowa sent a Blackhawk helicopter Sunday to drop roughly 1,000-pound sandbags on the levee, Hill said, adding it was too dangerous to use ground crews. It was not known how long the work would take.

"It's a technique that's been used before by the corps," he said. "There's no guarantees but we hope it will (work)."

Rhonda Wiley, emergency management director for Atchison County, Mo., said another nearby levee had a similar break Saturday, but Wiley said crews were able to repair it. She said levees along the Missouri River have been weakened by the river's recent high water levels.

"We anticipate these compromises rearing their ugly heads all up and down the levee system throughout this event," Wiley said Sunday. "It's not a pretty picture. But today nobody appears to be in imminent danger at this moment."

Hill said he wasn't aware of a previous leak but said some potential problems were spotted with the levee Saturday and were addressed. He didn't elaborate on the nature of those problems.

In South Dakota, the Army Corps of Engineers began construction of a backup levee Sunday to protect the town of Dakota Dunes. Corps engineer LeeJay Templeton said the 1.4-mile long secondary levee is slated to be completed by Thursday.

The Missouri River was expected to rise about 8 feet to 1,098 feet above sea level by June 14 in the city of about 2,500 people, some of whom have evacuated ahead of the planned crest. Officials said construction of the primary levee is still under way to protect the city 2 feet beyond the projected high level.

The levee leak affecting Hamburg is about five miles southwest of the city. Hill said that because the land is flat, any water pouring through will back up into Hamburg.

Mike Crecelius, emergency management coordinator for Fremont County, said no one really knows what's going to happen in Hamburg or where the incoming water will go.

"The situation down there is really unstable," he said.

Hill said the evacuation order was a precaution in case the levee is fully breached but he believes it was the appropriate call.

"The emergency manager in that area is being proactive," he said. "They know it takes a while to move 600 people."

Last week, Bond said Hamburg residents were told not to rely on the levee to protect the city. Fremont County officials requested 130,000 sandbags from the corps.

This year could be one of the wettest on record in the Missouri River basin, according to the corps. Officials are predicting record river flows and large releases from reservoirs in the Dakotas because of steady spring rain and above-normal snowpack. The corps has warned that the overflowing river isn't likely to crest until mid- to late June and water will remain high for weeks or even months.

The corps predicts the river will crest at 27 feet or higher in Nebraska City, Neb., which is across the river from Hamburg. Flood stage is 18 feet. As of Sunday afternoon, the river was at 23.14 feet at Nebraska City, according to the National Weather Service.


Associated Press Maria Fisher in Kansas City, Mo. contributed to this report. Ross reported from Omaha, Neb. She can be reached at http://twitter.com/timberlysross .