POPLAR BLUFF, Mo. (AP) - 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 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 residents 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, calling it a "miracle" that the first hole did not develop until late morning.

In another area near the confluence of the swollen Mississippi and Ohio rivers, authorities debated a desperate plan to use explosives to blow a 2-mile-wide hole through a levee to ease the pressure on others.

Butler County Sheriff Mark Dodd said the water pouring through the levee was unlikely to make it far enough upstream to add to the threat facing Poplar Bluff, where about 1,000 homes had already been evacuated. But authorities planned to evacuate more homes closer to the breach, which was in a sparsely populated area.

Despite the punishment the region has already endured, the weather was expected to get worse - and soon. Another line of storms 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.

The storm system dumped heavy rain on seven states and spawned at least one tornado Monday in Arkansas. The twister killed four people and blasted a path of destruction through the town of Vilonia, 25 miles north of Little Rock. Four others died in floods.

In Mississippi, a 3-year-old girl was killed when a storm toppled a tree onto her home. And in the sleepy town of Smithland, Ky., residents fled their homes while hundreds of volunteers piled sandbags along the riverfront. The water was rising 6 inches a day.

• Meanwhile, heavy rains have caused floods, blackouts, landslides and at least one death in Rio de Janeiro.

The city's emergency operations center reports on its website that the storm Monday night flooded several downtown streets and the Maracana stadium, site of the final game of the 2014 World Cup and major ceremonies of the 2016 Olympic games. A body was found in a flooded area downtown.