POPLAR BLUFF, Mo. – Floodwaters threatened earthen levees protecting thousands of homes in the nation’s midsection Tuesday, rising so fast in some places that panicked residents didn’t have time to pile up sandbags.

Storms have unleashed more than a foot of rain across the region, and the forecast offered little hope for relief. Another, larger storm system was brewing along the same path, bringing several more days of rain and the possibility of tornadoes.

The greatest flooding threat loomed in the southeastern Missouri community of Poplar Bluff, a town of 17,000 about 130 miles south of St. Louis. Six inches of rain fell Monday alone, bringing the four-day total to 15 inches.

By midday, the deluge had caused the Black River to pour over a levee in 30 places. The flood wall extending from Poplar Bluff to the town of Qulin downstream was also breached in at least one place, allowing water to gush through a hole.

“Each heavy downpour, each hour that passes by with the water pushing on that levee, the likelihood of a failure is that much more possible,” said Deputy Police Chief Jeff Rolland.

In another area near the confluence of the swollen Mississippi and Ohio rivers, authorities debated a desperate plan to blow up one levee to ease the pressure on others.

Despite the punishment the region has already endured, the weather was expected to get worse — and soon. A second system moving through Oklahoma and Texas carried the same threat of tornadoes and flooding but over a broader area that stretched from Dallas to Louisiana and up to Memphis.

Greg Corbin, the warning coordination meteorologist for the National Weather Service’s Storm Prediction Center in Norman, Okla., said having two such storms in such rapid succession is unusual.