As the death toll from days of heavy rain in the US Midwest is rising, the Illinois National Guard has been ordered to take action.

"I have ordered Illinois National Guard soldiers into active duty to aid local efforts to save lives and mitigate flood damage in Southern IL," Illinois Governor Bruce Rauner, who toured some of the affected communities, tweeted Friday.

According to news reports, 23 people have died so far in the Midwest, including fifteen in Missouri and eight in Illinois.

The reports also show that the toll could still rise, as the fate of two missing Illinois teenagers last seen several days ago is still unknown.

On Friday, hundreds of people were urged to flee rising floodwaters after swathes of the United States have been struck in the last week by tornadoes, storms and torrential rain.

Many people have to be relocated as their homes have been either damaged or wiped out completely.

"We're just basically homeless. We have nowhere to go," Damon Thorne, 44, told ABC News.

Forecasters have predicted that southern US states will face increasingly grave danger in the coming days.

"Major flooding is occurring or forecast on the Mississippi and Ohio rivers and tributaries in Missouri, Illinois, and Kentucky, with record flooding at several locations," the National Weather Service said.

"Major flooding is also occurring on the Arkansas River and tributaries in Arkansas. Floodwaters will move downstream over the next couple of weeks, with significant river flooding expected for the lower Mississippi into mid-January."

There are also fears among southern Illinois’ residents, as the rising Mississippi River has reportedly topped a levee, threatening several towns and rural communities.

"All that water's coming south and we have to be ready for it," Louisiana Lieutenant Governor-Elect Billy Nungesser told CNN. "It's a serious concern. It's early in the season. We usually don't see this until much later."