Record flooding from the rain-swollen Mississippi River and its tributaries stressed dams and levees to the breaking point in parts of Illinois, one of several central US states reeling from winter storms that have killed some two dozen people.

As national guardsmen began helping hundreds of Illinois residents flee rising floodwaters, authorities warned Saturday that levees in the state were under stress and that those along the entire Mississippi River were near capacity.

Authorities said they were continuing to search for more victims as the death toll continued to mount after several days of heavy rain deluged vast area of the US Midwest.

The National Weather Service warned that a flash flood watch in affected areas would remain in place through late Sunday.

Swaths of the United States have been buffeted over the holiday season by tornadoes, storms and torrential rain, while the US East Coast has seen unseasonably warm weather.

Missouri and Illinois have been particularly hard hit by the record-breaking and relentless deluge, with many river levels in the area at all-time highs.

The death toll from the flooding in the Midwest is now at 23, CNN said. Fifteen of the dead were in Missouri and eight in Illinois.

But the toll could rise, with increasing concerns about the fate of a missing Illinois teenager last seen several days ago.

Authorities said they have recovered the body of another teen who also went missing in the deluge.

There were growing fears too for residents in southern Illinois, where the rising Mississippi River reportedly topped a levee, putting several towns and rural communities at risk.

In all, 11 levees have failed in Illinois and Missouri, the Chicago Tribune reported. The Weather Service urged people to follow evacuation orders, saying levee failures could lead to "sudden and potentially deadly flooding."

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

Forecasters warned that southern US states were in increasing danger in the days and even weeks to come.

"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 was some relief, however, in the St. Louis area of Missouri, where flooding was at last receding.

For many, the big cleanup now begins. The less fortunate saw their homes wiped out.

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

He and his 60-year-old mother Linda were staying at a Red Cross shelter at a church after their mobile home park in Arnold, Missouri was washed away by the surging Meramec River.

Meanwhile, the year-end storms also were taking a toll on US agriculture, media reported.

In Texas, thousands of cows died in a surprise blizzard, while the milk supply dried up for thousands of others went unmilked for several days, reducing their production for months to come, dairy officials told CNN.