Thousands of Arkansas and Oklahoma residents braced for more flooding on Wednesday and some evacuated their homes, as forecasts of further rain drove fears that decades-old levees girding the Arkansas River may not hold.
More than a week of violent weather, including downpours and deadly tornadoes, has lashed the central United States, bringing record-breaking floods in parts of the two states, turning highways into lakes and submerging all but the roofs of some homes.
"This is a flood of historic magnitude," Arkansas Governor Asa Hutchinson told a news conference on Wednesday, joined by state and federal emergency officials. Of the Arkansas River, he said: "It's a beautiful sight until it comes to get you."
Flooding has already closed 12 state highways, the governor said, and 400 households have agreed to voluntary evacuations.
Hutchinson sent a letter to President Donald Trump on Wednesday, asking for a federal emergency declaration for Arkansas.
The levee system along the Arkansas River "has not seen this type of record flooding" before, Hutchinson said in his six-page letter.
More heavy downpours are forecast through Wednesday night over much of Oklahoma and Arkansas, with between 1 and 3 inches (2.5 to 7.6 cm) expected, said Patrick Burke, a meteorologist at the National Weather Service's Weather Prediction Center.
By early June, rivers are expected to crest to the highest levels on record all the way down to Little Rock, Arkansas, Burke said.
In Tulsa, Oklahoma's second largest city, Mayor G.T. Bynum warned that the city's levees were being tested "in a way that they have never been before."
So far, he said, the 20-mile (32 km) levee system, which protects some 10,000 people, was working as designed and being patrolled around the clock by the Oklahoma National Guard.
Staff at the Harvest Church West Tulsa, which sits behind a levee a few blocks from the Arkansas River, moved furniture and sound and office equipment from the basement to the church's second floor and relocated staff out of the neighborhood.
"For levees that are 70 years old, they're holding well but they're not designed to hold the pressure this long, which is what the fear is at this point," Chuck Barrineau, the church's lead pastor, said in a phone interview.
At least six people have died in the latest round of flooding and storms in Oklahoma, according to the state's Department of Health.
More than 300 tornadoes have touched down in the Midwest in the last two weeks. Tornadoes pulverized buildings in western Ohio on Monday, killing one person and injuring scores of others.