Storm-strained levees protecting a Missouri town threatened to give way Tuesday as a severe weather system continued to pound the Midwest and Arkansas, where seven people were killed overnight in an outbreak of violent rainstorms and tornadoes.

People in Poplar Bluff, Mo., were “living inch by inch, hour by hour,” said Deputy Police Chief Jeff Rolland. It was a miracle that the levee there was still holding back the Black River, he added, though water was spilling over the top in about 30 locations.

The town of 17,000 residents 130 miles south of St. Louis was the worst-hit of several areas in the Mississippi and Ohio River valleys that were threatened by floodwaters. A dam in St. Francis County, about 40 miles south of St. Louis, was also in jeopardy of bursting, and levees strained to contain floodwaters in Pike and Lincoln counties, along the Mississippi River north of St. Louis.

In Arkansas, authorities said three people were killed when floodwaters swept two vehicles off of roadways and four others died when a twister — which residents described as a half-mile wide — ripped through the small town of Vilonia.

“The town’s gone,” Vilonia resident Sheldon Brock said outside a gas station a few miles outside of town.

Stephan Hawks, a spokesman for the sheriff’s office in Faulkner County, where Vilonia is located, said a roof was blown off the local grocery store, and power poles snapped like toothpicks. Rescuers were looking for survivors in the wreckage.

“Right now, just in the town, there are 14 to 16 houses that have been destroyed,” Hawks said. “We’re not real sure where those people are. We don’t think they’re in the houses. We’re trying to locate them, approximately 50 to 60 people.

“A big hindrance, I’m afraid, is the 80 percent chance of storms we’re going to get this afternoon. They just keep on coming,” he added.

Tommy Jackson, a spokesman for the Arkansas Department of Emergency Management, said people were racing to prepare for the next round of severe weather, “but there’ll be many, many volunteers there helping out their fellow residents.”

In northwestern Arkansas’ Madison County, emergency management coordinator Lori McConnell said a man and a woman died after floodwaters swept their car off the road. In neighboring Washington County, sheriff’s spokesman Kelly Cantrell said a woman died when her vehicle was swept off Arkansas 265 in the southern part of the county. The woman’s 11-year-old son survived.

Forecasters have said the rain and storms that began early last week and have hammered a swath of the nation’s midsection could continue for days in some places. Powerful storms ravaged Missouri, Arkansas, Kentucky, Texas, Tennessee and other states on Monday.

In Kentucky, widespread power outages closed many schools and businesses, and thousands of residents were still without electricity Tuesday. Emergency management officials said hundreds of trees and power lines were uprooted after winds overnight that topped 100 mph in some counties.

Joe Muncy of Murray, Ky., was out clearing a tree that fell on part of his house. He said he was awakened by the noise just after midnight.

“And I mean, I was scared. And of course … you can’t go outside and see what’s going on,” Muncy said.

Governors in both Arkansas and Kentucky have declared states of emergency. In Kentucky, historic flooding is expected over the next few days from the Ohio and Mississippi rivers. Several dozen residents were evacuated near the confluence of the rivers at Cairo, Ill.

The U.S. Army Corps of Engineers was considering the extraordinary step of intentionally breaching the Birds Point levee in southeast Missouri, just downriver of the confluence, in a bid to reduce the amount of water moving down the Mississippi. The move would soak 130,000 acres of farmland, and Missouri Gov. Jay Nixon objected to the idea. A decision was expected Tuesday.

The storm system was expected to move into Illinois and Wisconsin on Tuesday, said Greg Carbin, a meteorologist with the Storm Prediction Center in Norman, Okla. At the same time, a second storm system will start along the same path, meaning several more days of rain. That system will continue east through Thursday, he said.

In the Poplar Bluff area, some 1,000 homes have been evacuated and 59 people were rescued late Monday after water overran the dam and inundated a section of the town, the deputy police chief said. No deaths or serious injuries have been reported.

Police officers spent Monday going door-to-door in the southwest part of town, telling residents to get out, but not everyone did. Along one road near the levee, children played knee-deep in water. Adults gathered on the porches, seemingly enjoying nature’s show.

Other residents were being more cautious. At least 150 took shelter at the town’s Black River Coliseum, a concert and meeting venue overlooking the swollen river. Hotels in town were full. Some displaced residents stayed with relatives.

Police Chief Danny Whiteley was hoping the water would recede soon enough that flooding would mostly be limited to basements. He wasn’t optimistic.

“I guess you’d call it a perfect storm: It’s just all come together at once,” Whiteley said.

Missouri was still cleaning up from tornado damage in the St. Louis area — 2,700 buildings, including Lambert Airport, were damaged in the Friday night twister.

Kelly MacNeil of member station KUAR in Little Rock, Ark., and Angela Hatton of member station WKMS in Murray, Ky., contributed to this report, which contains material from The Associated Press. Copyright 2011 National Public Radio. To see more, visit http://www.npr.org/.