Torrential rains over the past several days have caused rare winter flooding across Missouri and Illinois, shutting down portions of two interstates on Tuesday and threatening hundreds of homes. 

Record flooding was projected at some Mississippi River towns, while the Meramec River near St. Louis was expected to get to more than 3 feet above the previous record by late this week.

Residents in the town of West Alton, Mo., were told Tuesday to evacuate after a levee reportedly failed along the Mississippi River during heavy rains across the state.

Mayor William Richter ordered the town's approximate 520 residents who had not already evacuated to get out of harm's way, the Associated Press reported.

At least 18 deaths in Missouri and Illinois are blamed on flooding, mostly involving vehicles that drove onto swamped roadways.

West Alton is about 20 miles north of St. Louis.

Missouri Gov. Jay Nixon activated the National Guard to assist with security in evacuated areas and to help divert traffic at road closure sites.

The U.S. Army Corps of Engineers said Tuesday that the rising Mississippi and its tributaries were threatening to overtop 19 federal levees in the St. Louis area. The threatened areas include Perry and Ste. Genevieve counties in Missouri, and Randolph County in Illinois. The levee protecting the historic downtown of Ste. Genevieve is not believed to be threatened.

In another eastern Missouri town, Union, water from the normally docile Bourbeuse River reached the roofs of a McDonald's, QuikTrip and several other businesses. The river reached an all-time high Tuesday, nearly 20 feet above flood stage.

Interstate 44 was closed Tuesday near the central Missouri town of Rolla, and a section of Interstate 70 was shut down in southern Illinois. Hundreds of smaller roads and highways were also closed across the two states, and flood warnings were in effect.

In St. Louis, more than 100 volunteers turned out in blustery, cold conditions to fill sandbags where a flooded waterway threatened hundreds of homes.

The River Des Peres is a man-made storm sewer channel that flows through south St. Louis into the Mississippi River, a few miles south of the Anheuser-Busch brewery. The channel is deep enough that flooding isn't a concern under normal conditions.

The Mississippi River is expected to reach nearly 15 feet above flood stage on Thursday at St. Louis, which would be the second-worst flood on record, behind only the devastating 1993 flood.

Maureen Hooch, 57, was among the volunteers at that 1993 flood, and she was out again Tuesday, this time under far different circumstances.

"The last time I was out here it was 1,000 degrees," Hooch told the Associated Press. "They had a bus you could get on to cool off. I prefer the cold. When you work, you warm up."

Alderman Larry Arnowitz said up to 500 homes could be threatened if the River Des Peres rises much more than projected.

He was confident that with no rain in the forecast for the next several days — and with the help of the thousands of sandbags — everything would be OK.

The high water was blamed on the shutdown of a wastewater treatment plant on Monday just south of St. Louis, causing sewage to go directly into nearby rivers and streams.

The Metropolitan Sewer District of St. Louis said the Fenton wastewater treatment plant, which is designed for 6.75 million gallons per day of flow, was treating nearly 24 million gallons per day at the time of the malfunction.

One of the two wastewater plants in Springfield, Missouri, also failed, allowing partially treated sewage to flow into a river.

The U.S. Coast Guard closed a 5-mile portion of the Mississippi River near St. Louis due to flooding. Capt. Martin Malloy cited high water levels and fast currents in the river, which is a vital transportation hub for barges that carry agricultural products and other goods.

In central and southern Illinois, flood warnings were in effect a day after a winter storm brought sleet and icy rain. Major flooding was occurring along the Kankakee, Illinois, Sangamon and Vermilion rivers.

An Illinois prison with nearly 3,700 inmates was preparing for possible flooding from the Mississippi River on Tuesday.

Illinois Department of Corrections spokeswoman Nicole Wilson says that employees and emergency work crews at the Menard Correctional Center near Chester are filling sandbags and "working around the clock."

The maximum security prison is on lockdown, and visits have been suspended. Officials also anticipate having to bring in hundreds of portable toilets in case the prison's water service is shut down.

In Granite City, Illinois, about 30 residents of a flooded trailer park idled in a Red Cross emergency shelter in a church basement. The park's property manager told Shirley Clark, 56, and other displaced residents that it could be another 10 to 12 days before they're able to return to their homes.

"We need help over here," said Clark, a diabetic who said she left behind her insulin supply. "We're just holding on."

The Associated Press contributed to this report.