(CNN) -- Missouri Gov. Jay Nixon ordered the state's National Guard to the southeastern corner of the state to help combat rising rivers as parts of the lower Mississippi and Ohio river valleys braced for what the National Weather Service said could be record flooding.
In Poplar Bluff, about 130 miles south of St. Louis, the swollen Black River threatened to break through a compromised levee, prompting police to order an emergency evacuation of the southeastern part of the town.
About 250 to 300 people living in the city of 17,045 were affected by the evacuation order, according to City Manager Doug Bagby. As many as 1,000 people could ultimately be affected, he said.
Police went house to house in part of Poplar Bluff on Monday, ordering people to evacuate ahead of what they said was an imminent "catastrophic failure" of a levee on the Black River.
The city said the levee had been compromised after a week in which the area received more than eight inches of rain. Authorities ordered some residents most at risk to evacuate immediately. Other residents near the river were asked to closely monitor developments and water levels in their neighborhoods, the police department said.
"The levee is weakening by the minute and may fail at any time," the National Weather Service said in an alert Monday afternoon.
The weather service said the southeastern portion of the city would be inundated if the levee fails.The levee protects Poplar Bluff from the river, which is now more than four feet over flood stage, according to the weather service.
Nixon ordered National Guard troops to help with efforts to shore up levees near Poplar Bluff and other river communities, among other duties.
The Red Cross has established a shelter at the Black River Coliseum, according to the police department. Twenty-five residents were at the shelter as of midday Monday, according to the city.
Poplar Bluff was under a flood warning from the National Weather Service. The agency said the Black River is expected to rise nearly another foot and a half before cresting Monday. But the Weather Service warned that river levels could rise even more if heavy rains forecast in the next few days materialize.
Concern over the levee comes as parts of the Mississippi and Ohio river valleys brace for what the National Weather Service said could be major flooding throughout the region. Some of the flooding could be record-setting, the agency said.
In Cape Girardeau, Missouri -- where the National Weather Service predicted that the Mississippi River would crest Friday at 12.5 feet above flood stage -- the city-owned airport had to close Sunday as standing water from heavy rains covered its runways.
The airport, which remained closed Monday, was activating a pumping system to clear the water, administrative coordinator Katrina Atkins said, but it was unclear when the airport might reopen as more heavy rain is forecast for the remainder of the week.