Rain-swollen rivers across Missouri were still rising on Wednesday, with widespread flooding forcing the evacuation of hundreds of people, closing part of a major interstate highway and threatening to wash out scores of structures.

At least 13 people have died in Missouri since the weekend, when days of downpours from a massive winter storm system triggered the worst flooding in two decades, Governor Jay Nixon said.

"It's very clear that Missouri is in the midst of a very historic and dangerous flooding event," Nixon said during a Tuesday news conference.

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Several major rivers and tributaries in Missouri and Illinois were poised to crest at record levels, the National Weather Service said. Some of the rivers would continue to rise until Saturday.

At the confluence of the Mississippi and Missouri rivers, about 20 miles north of St. Louis, residents of the towns West Alton and Arnold were told to evacuate on Tuesday.

Flooding in the middle portion of the Mississippi River and its tributaries may reach the highest levels in recorded history, the forecasting site AccuWeather said.

The U.S. Coast Guard closed a five-mile stretch of the Mississippi River near St. Louis to all vessel traffic due to hazardous conditions.

The National Weather Service forecast the Mississippi River at the Chester, Illinois, river gauge about 60 miles south of St. Louis would crest at 49.7 feet on Friday – matching the 1993 record.

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The floodwaters have forced the closured of roadways and highways, including a portion of Interstate 44, a major highway that runs from west Texas to St. Louis, the Missouri Department of Transportation said on Wednesday.

Sewage has been flowing into the fast-rising Meramec River near St. Louis since Monday, when floodwater disabled a sewer treatment plant, the St. Louis Post-Dispatch reported.

In Illinois, some inmates were moved out of the Menard Correctional Center, a maximum security prison on the banks of the Mississippi River, and sandbags and drinking water were prepared in anticipation of flooding in lower level cell blocks, Illinois officials said in a statement.