The flooding, which started last week, has killed five people
, said Mike O'Connell of the Missouri state highway patrol. It has inundated homes and businesses, and led to the closing of 272 roads.
Along the Meramec River in Eureka, residents piled up sandbags to protect homes and businesses. Heavy rains in the St. Louis area Wednesday sent the river bulging to a record of 46.11 feet.
Forecasters said up to 4 inches of rain will fall in the saturated St. Louis area.
Residents should treat the flooding like a "liquid blizzard" and stay home, said Karen Yeomans of the Missouri Department of Transportation.
'Never seen it this bad'
Shayla Kremer shared several photos from Pacific, Missouri, showing homes and streets underwater because of flooding from the Meramec River.
Kristen Wingerter Martinez said residents in Eureka are confined to the city after roads shut down.
"My husband has lived in Eureka since 1972, never seen it this bad," Martinez said. "Kids are out of school. People can't make it to work. National Guard brought in. A community pulling together to save our favorite pizza place. Elks lodge feeding all the volunteers with the American flag flying high in Eureka."
Eureka police Chief Michael A. Wiegand urged residents to follow instructions.
"This is some of the highest water we have ever seen and it will be higher than 2015," he told CNN affiliate KTVI.
"We need to all use our common sense. Don't drown turn around, if you see standing water don't drive through it whatsoever."
Four St. Louis County school districts will remain closed through Thursday, citing concerns about student safety and transportation in the event of flooding. Lindbergh, Mehlville, Northwest and Rockwood school districts have all closed.
"I'm aware of many employees who live in areas affected by this natural disaster. We simply cannot open our schools with the current shortage of bus drivers, teachers and support staff," Rockwood School Districts Superintendent Dr. Eric Knost said in a statement.
To get to Eureka High School, where Knost spent his day Tuesday, he had to get assistance from the US Coast Guard in a boat.
"Our employees will be on site around the clock, attending to the ever-changing situation," he said. "We are trying to hold waters back as we approach the flood's crest and even more rain and storms are heading our way."
Gov. Eric Greitens declared a state of emergency April 29.
Our administration is taking a new approach to disaster response: "Go big and go early," he said.
Other states affected
The National Weather Service said flood warnings would likely be extended in parts of Oklahoma, northern Arkansas, Illinois and Indiana.
"Many of the rivers in these states have crested or (are) nearing crest and remain in moderate or major flood category. Many roads across this region are closed because of the flooding," it said.