People walk on a road in Vilonia, Ark., on Tuesday after a tornado hit the area late Monday. The storm system killed at least nine people, including four who drowned in floods. Danny Johnston/Associated Press

A powerful storm system that spawned a deadly tornado in Arkansas caused rivers to swell Tuesday across the Midwest, straining levees that protect thousands of homes and forcing panicked residents of one town to flee for higher ground.

Fifteen centimetres of rain fell Monday in the southeastern Missouri community of Poplar Bluff, bringing the four-day total to 40 centimetres. The deluge caused the Black River to pour over a levee in 30 places, and about 1,000 homes had to be evacuated.

Deputy Police Chief Jeff Rolland said it was a "miracle" the levee had held until late morning. He credited emergency crews for their work to bolster weakened areas of the barrier and for evacuating residents.

The levee extended from Poplar Bluff to the town of Qulan downstream, in a sparsely populated area.

Butler County Sheriff Mark Dodd said water pouring through the breach between the two towns was unlikely to make it far enough upstream to threaten Poplar Bluff, a town of 17,000 about 200 kilometres south of St. Louis. Authorities planned to evacuate only homes closest to the breach.

The storm system has dumped relentless rain on several states over the past week, including Arkansas, Illinois, Indiana, Kentucky, Missouri, Mississippi and Tennessee.

More storms coming

As the worst of the system moved north and east into Illinois, Wisconsin, Kentucky and Tennessee, the region was bracing for a second round of storms expected to roll into Oklahoma and Arkansas later Tuesday.

The storms spawned at least one tornado Monday in Arkansas that killed four people and carved a wide swath of destruction through the town of Vilonia, 40 kilometres north Little Rock. And flooding in other parts of the state caused at least five other deaths.

The U.S. National Weather Service office in North Little Rock sent survey teams to Vilonia and nearby Garland County to investigate the damage from Monday's storm and assess how much of it was caused by tornados or straight-line winds.

John Robinson, a weather service warning co-ordination meteorologist, said it could take days.

"It wouldn't surprise me if we were to end up with a count of 10 or 12 tornadoes by the time all the surveys are completed," Robinson said.

Authorities in Mississippi say a three-year-old girl in the city of McComb was killed when a storm from the same system toppled a large tree into her family's home. The girl's parents, who were in the room with her, were both injured.

More showers and thunderstorms were expected in the area on Tuesday, giving crews that worked overnight to sure-up the levee no rest.

Rolland said street department workers hurriedly filled small boats with sandbags overnight and were able to sure up a vulnerable section of the levee in Popular Bluff.

Crews rescued 59 people in 1½ hours late Monday after water spilled over the dam.

A full-scale levee breach could force the evacuation of about 6,000 homes from Poplar Bluff to Qulin and destroy or severely damage 500 homes in Poplar Bluff and its outskirts, Rolland said.