Authorities were scrambling Tuesday to protect the town of Hamburg, Ia., after a swollen Missouri River broke two levees near the Missouri-Iowa border.

Fifty Army National Guard troops arrived in Hamburg Monday night to join efforts to finish a temporary levee before water from the levee breaches can reach the town — expected to happen sometime Tuesday, according to CNN affiliate KMTV. Crews are working to add another three feet to the top of the temporary levee, KMTV said. If the temporary levee does not hold, parts of Hamburg could be inundated with up to 10 feet of water.

The Iowa Department of Transportation closed one half-mile lane of northbound Interstate 29 while the work was underway, it said Monday. Floodwaters are expected to inundate the roadway within 48 hours, it said.

The current levees protecting Hamburg were designed to an elevation of 916 feet, the Corps of Engineers said in a statement Monday. “Based on the current size, new staff gauges and the model calibrated to new survey data, a new water surface elevation of 918 feet has been estimated,” according to the Corps.

The levee’s operators “will proceed with a breach to a downstream portion of the levee” in an effort to delay the time in which the 916-foot elevation will be reached, the Corps said.

The Iowa Homeland Security and Emergency Management Division is working with “multiple state agencies and private companies” in transporting materials to build up the secondary levee, Iowa Gov. Terry Branstad’s office said in a statement Monday night.

The first breach, which occurred Monday morning, was some 300 feet wide and growing as of Monday night. It was located in Atchison County, Mo., just south of Hamburg, officials said.

The second breach was located south of Atchison, in Holt County, Mo., said Holt County clerk Kathy Kunkel. Flooding was affecting farmland, she said.

A breach earlier this month had prompted the evacuation of hundreds of people in Hamburg. While no evacuations were ordered or recommended because of Monday’s breach, many people have not returned to their homes, KMTV said.

“I’m without a home, living with my kids,” resident Robert Reafleng told KMTV. “All of my stuff is in a semi. I have no job. Where I work, they closed up.”

The breach near Hamburg was deemed too substantial to repair, said David Pearson with the National Weather Service in Omaha, Nebraska. “The next step is to attempt to mitigate the flooding with another levee between the one that failed and Hamburg.”

It was too early to determine the cause of the breach near Hamburg, the Corps said. But it follows weeks of high flows and record releases from dams in Montana and the Dakotas. Heavy rains and snowpack runoff could result in near-record flooding along parts of the Missouri this year, officials have said.

This year’s flooding is putting levees to the test along much of the 1,700 miles of the Missouri. Temporary levees are being built in several locations.