Tornadoes rolled in from the prairie and slammed Oklahoma City and its suburbs, trapping people in their vehicles as a storm swept down an interstate highway while commuters tried to beat it home.
Five people were killed, including a mother and baby killed near Union City. Another person died at El Reno, the first city struck by the storm, said Amy Elliott, a spokeswoman for the state medical examiner. Circumstances involving the other two deaths weren't immediately known, Elliott said.
About 50 people were hurt, five critically, hospital officials said.
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Meteorologists had warned about particularly nasty weather Friday but said the storm's fury didn't match that of a deadly twister that struck suburban Moore last week. Violent weather also moved through the St. Louis area, ripping part of the roof off a suburban casino.
Friday's broad storm in Oklahoma hit during the evening rush hour and stuck around, causing havoc on Interstate 40, a major artery connecting suburbs east and west of the city, and dropping so much rain on the area that streets were flooded to a depth of 4 feet.
To the south, a severe storm with winds approaching 80 mph rolled into Moore, where a top-of-the-scale EF5 tornado killed 24 on May 20.
Rick Smith, the warning coordination meteorologist for the National Weather Service at Norman, said that while the storm packed a powerful punch, it wasn't as strong as the Moore tornado.
"This storm had everything you could handle at one time: tornadoes, hail, lightning, heavy rain, people clogging the highways," Smith said.
The region was fortunate because the storm touched down mostly in rural areas and missed central Oklahoma City.
"It's not even close to anything like what we had last week," Smith said. "We were very concerned this would move into downtown. It would have been a major problem. It made all the difference that it was out in the country."
The U.S. averages more than 1,200 tornadoes a year and most are relatively small. Of the 60 EF5 tornadoes to hit since 1950, Oklahoma and Alabama have been hit the most -- seven times each.
Heavy rain and hail hampered rescue efforts in Oklahoma City. Frequent lightning roiled the skies well after the main threat had moved east. Highways and streets were clogged late into the night as motorists worked their way around flooded portions of the city. Will Rogers World Airport said flights wouldn't resume until morning, after debris was cleared from runways.
Oklahoma Highway Patrol Trooper Betsy Randolph said troopers found the bodies of a woman and an infant near their vehicle. Randolph said it's not known if the woman was driving into the storm when it hit around 7 p.m. Friday.
Emergency officials reported that numerous injuries occurred in the area along I-40, and Randolph said there were toppled and wrecked cars littering the area. Troopers requested a number of ambulances at I-40 near Yukon, west of Oklahoma City.
The storm picked up and threw a Weather Channel Tornado Hunt chase vehicle. The Hunt Team is safe but has minor injuries, the Weather Channel reported.
"We're scrambling around," said Lara O'Leary, a spokeswoman for the local ambulance agency. "There is very low visibility with the heavy rain ... so we're having trouble getting around.
Standing water was several feet deep, and in some places it looked more like a hurricane had passed through than a tornado.
In Missouri, the combination of high water and fallen power lines closed dozen of roads, snarling traffic on highways and side streets in the St. Louis area. At the Hollywood Casino in suburban of Maryland Heights, gamblers rushed from the floor as a storm blew out windows and tore off part of the roof.
Rich Gordon, of Jefferson City, said he was on the casino floor when he heard a loud "boom."
"I didn't know if it was lightning or what, but it was loud," Gordon said.
In Oklahoma, storm chasers with cameras in their cars transmitted video showing a number of funnels dropping from the supercell thunderstorm as it passed south of El Reno and into Oklahoma City just south of downtown. Police urged motorists to leave I-40 and seek a safe place.
"I'm in a car running from the tornado," said Amy Sharp, who last week pulled her fourth-grade daughter from the Plaza Towers Elementary School as a storm approached with 210 mph winds. "I'm in Norman and it just hit Yukon where I was staying" since last week's storm.
"I'm with my children who wanted their mother out of that town," Sharp said, her voice quivering with emotion.
At Will Rogers, passengers were directed into underground tunnels as the storm passed just north of the airfield. However, people near the area said they weren't aware of any damage.
Television cameras showed debris falling from the sky west of Oklahoma City and power transformers being knocked out by high winds across a wider area.
As the storm bore down on suburban Oklahoma City, Adrian Lillard, 28, of The Village, went to the basement of her mother's office building with a friend, her nieces, nephews and two dogs.
"My brother's house was in Moore, so it makes you take more immediate action," Lillard said while her young nieces played on a blanket on the floor of the parking garage. "We brought toys and snacks to try our best to keep them comfortable."
Well before Oklahoma's first thunderstorms fired up at late afternoon, the Storm Prediction Center in Norman was already forecasting a violent evening. From the Texas border to near Joplin, Mo., residents were told to keep an eye to the sky and an ear out for sirens.
Friday evening's weather came after flash flooding and tornadoes killed three people in Arkansas late Thursday and early Friday. Three others were missing in floods that followed 6 inches of rain in the rugged Ouachita Mountains near Y City, 125 miles west of Little Rock.
This spring's tornado season got a late start, with unusually cool weather keeping funnel clouds at bay until mid-May. The season usually starts in March and then ramps up for the next couple of months.
Associated Press writers Ken Miller and Tim Talley in Oklahoma City, Justin Juozapavicius in Tulsa; Jeannie Nuss in Texarkana, Texas; and Jim Salter in Maryland Heights, Mo.; and freelance photographer Nick Oxfrod in Oklahoma City contributed to this report.