Large clouds are seen as a tornado passes south of El Reno, Oklahoma May 31, 2013. [Photo/Agencies]

CITYWIDE FLOODING

Tim Oram, meteorologist for the National Weather Service, said it was difficult to know exactly how many tornadoes had touched down, but three major thunderstorms with the potential to produce tornadoes moved through the center of the state.

The service later lifted a tornado warning for Oklahoma City and surrounding areas, as flash floods in the wake of the storms dunked parts of the sprawling metropolitan area - home to more than 1.3 million people - under water.

Storms also swept into neighboring Missouri, where Governor Jay Nixon declared a state of emergency on the heels of what he said was several days of heavy rain.

Winds turned over semi-trailer trucks on Interstate 70 between St. Louis and St. Charles County to the west, said Brett Lord-Castillo, spokesman for the St. Louis County Emergency Management Agency.

Hollywood Casino in Maryland Heights was evacuated when part of its roof was blown off, Lord-Castillo said. No deaths or serious injuries were reported in the greater St. Louis area.

Power utilities Oklahoma Gas and Electric and Ameren said 200,000 customers were without power in Oklahoma, Missouri and Illinois, which had been under a tornado warning on Thursday.

On Thursday, storms in Oklahoma and Arkansas killed at least three people, including Scott County, Arkansas, Sheriff Cody Carpenter, whose body was recovered early on Friday, said a spokesman for the Arkansas Game and Fish Commission.

A man also died in Tull, Arkansas, when a tree fell on his car, and a woman's body was found in flood waters in Scott County on Friday.

Large, long-lasting thunderstorms known as supercells are responsible for producing the strongest tornadoes, along with large hail and other dangerous winds.