A slow-moving storm system is bringing the threat of flash floods to tens of millions of Americans Thursday from Texas all the way to Illinois after severe storms earlier this week left 2 dead in Oklahoma.

The National Weather Service's Weather Prediction Center said that widespread showers and storms are expected throughout the day, with the risk of "excessive rainfall" over parts of those areas over the next couple of days.

"Numerous showers and storms are expected to continue regenerating in the vicinity of this front with the best prospects for heavy rainfall from central Texas to southern Illinois, with amounts on the order of 2 to 4 inches likely for some areas," the NWS said.

A moderate risk of excessive rainfall exists through North Texas on Thursday. (National Weather Service)

Besides heavy rain, there is also the risk of severe thunderstorms across Texas and into the Ohio Valley.

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Heavy rain and thunderstorms overnight spawned flooding across North Texas, with lighting being blamed for causing four fires in Murphy, Texas.

The heavy rain caused flooding at the First Baptist Church of Lavon, where members were still cleaning up damage from flooding last week.

Heavy rain caused flooding at the First Baptist Church of Lavon in the Dallas area late Wednesday. (FOX4)

Pastor Brad Patterson told FOX4 that members put tarps and sandbags out to try to stop the water coming in, but several inches of water still got inside.

“You can still see water coming all the way up. I mean, 10 feet down this hallway and in this room as well,” Patterson told FOX4.

In Missouri, voluntary evacuations were issued for residents in West Alton due to rising waters on the Mississippi River that may crest at 35.5 feet, the fourth-highest of all time, FOX2 reported.

Burlington City workers Chadley Kilbride, left and Will Buhmeyer secure the upright beams for a portion of the expanded flood wall, while secured in harnesses Wednesday May 1, 2019 along the Mississippi Riverfront in Burlington, Iowa. (John Lovretta/The Hawk Eye via AP)

The St. Louis region has already seen between 2 to 5 inches of rain, with more expected by the weekend.

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The storms affecting Texas and the rest of the Midwest come after a man and woman were killed in separate incidents when severe storms swept across Oklahoma.

A 55-year-old man's body was found Wednesday inside his vehicle in Tulsa after it was submerged in floodwaters Tuesday night. He has not been identified.

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The vehicle was reported missing about 8 p.m. when water in the area was up to 20 feet deep. A passerby spotted the vehicle Wednesday.

In Bryan County, officials said a 58-year-old woman died when her home was destroyed by high winds near Bokchito, about 160 miles southeast of Oklahoma City. A tornado was reported there about 9 p.m. Tuesday.

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The NWS said at least 16 tornadoes were reported Tuesday in Oklahoma. Storms also spawned tornadoes in Texas and Arkansas.

Hospitals in southeast Oklahoma reported at least 22 people were injured as a result of Tuesday night's storms, according to the State Department of Health.

The Associated Press contributed to this report.