Missouri Governor Jay Nixon on Saturday toured communities ravaged by flooding that killed at least 31 people in several states and forced large-scale evacuations, as the danger of rising waters shifted to Arkansas and beyond.

Nixon visited Eureka and Cape Girardeau in eastern Missouri, where floodwaters caused widespread damage, and announced the federal government had approved his request to declare an emergency to help with the massive cleanup and recovery now under way. The governor described the scale of the flood damage as other worldly.

"It's almost as if you're living on some other planet," he said, standing near a growing pile of debris in a park in Eureka, about an hour's drive west of St. Louis on the banks of the Meramec River, which flows into the Mississippi.

"This is just a tiny fraction of the trail of destruction," the governor told reporters.

The National Weather Service reported Mississippi floodwaters in Illinois and Missouri began cresting and receding on Saturday after thousands of people had to be evacuated from their homes earlier in the week when the floods destroyed hundreds of structures.

Retired Eureka homeowner Tracy Wolf, 58, spent the last three days trying to keep water away from the sides of his house with sandbags and out of his basement with vacuums.

"Wednesday night it came in through the windows," Wolf said. "We slept three hours the first night ... I don't even know what day it is."

Twelve counties have been declared disaster areas in Illinois, where Governor Bruce Rauner on Saturday toured several communities hard-hit by flooding. On Friday, he ordered Illinois National Guard troops into flooded areas to mitigate damage and help with evacuation.

At least 31 killed

The floods claimed the lives of at least 31 people in Illinois, Missouri, Oklahoma and Arkansas, most of whom drove into flooded areas after days of downpours.

Authorities continued searching on Saturday for country singer Craig Strickland of the band Backroad Anthem. He had gone duck hunting on an Oklahoma lake during stormy conditions and his friend, Chase Morland, was found dead on Monday.

In Thebes, Illinois, about 201 km downriver from St. Louis, the floodwater was expected to crest at 14 m on Sunday, more than 0.5 meters above the 1995 record, the NWS said.

Major flooding continued in the state of Arkansas along the Arkansas River and its tributaries.

Arkansas officials said they expected the river, which bisects the state from west to southeast before joining the Mississippi, to crest late on Saturday.

Large swaths of parkland in Little Rock along the river were covered with floodwaters, and some homes and farmland in the Arkansas Delta were flooded on Saturday.

Signs that floodwaters were headed south began to emerge as the NWS issued a major flooding designation on Saturday for Osceola, Arkansas, where the Mississippi River reached above 10.7 m, well above the 8.5 m flood stage.

The NWS also on Saturday warned communities in the Southern Mississippi Valley region of potential flooding during the next 10 days.