Nine people were killed in tornadoes that swept through central Oklahoma on Friday, part of a storm system that caused widespread flooding in Oklahoma City and its suburbs the state's chief medical examiner said on Saturday.
Among the dead were two children and seven adults, said Amy Elliott, a spokeswoman for the medical examiner's office. Two of the victims remain unidentified and officials said the names of those killed would not be released until their next of kin were notified.
Severe storms also swept into neighbouring Missouri.
Scott Holste, a spokesman for Missouri Governor Jay Nixon said three people had died in flooding, one of them a young man who was swept into a storm drain in Miller County.
The tornadoes struck just 11 days after a twister categorized as EF5, the most powerful ranking, tore through the Oklahoma City suburb of Moore and killed 24 people.
The latest storms dumped up to 8 inches (20 cm) of rain on the Oklahoma City area, causing flash flooding that submerged parts of the sprawling metropolitan area that is home to more than 1.3 million people.
Nearly two dozen people were rescued from areas cut off by rising water, the National Weather Service said. More than 70 people have been treated for storm-related injuries, Oklahoma hospital officials said.
The devastation was caused by large, long-lasting thunderstorms known as super cells, which produce the strongest tornadoes, along with large hail.
"Five tornadoes touched down in central Oklahoma, with the most powerful being an EF3 that struck near the rural community of El Reno 25 miles (40 km) west of Oklahoma City," said meteorologist Brynn Kerr of the National Weather Service's Storm Prediction Centre in the suburb of Norman.
"A much weaker tornado touched down in Moore," he added.
Moore had limited damage, a police dispatcher said.
The tornadoes hit during the evening rush hour and many of those hurt or killed were on the roadways.
Among the dead were a woman and her baby who were traveling on Interstate 40, just west of Oklahoma City, when their vehicle was picked up by the storm and they were sucked out of it, said Betsy Randolph, spokeswoman for the Oklahoma Highway Patrol.
One tornado rampaged down the interstate, tipping over trucks and hurling hay bales, a witness said. Television images showed downed power lines, tossed cars and motorists stranded in flood water.
In some parts of central Oklahoma, homes were destroyed, roofs were torn off and power lines were ripped down. Work crews were repairing washed-out patches of roadways and removing downed trees in order to allow aid workers to get through.
"In Missouri, violent winds flipped 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.
Power utilities Oklahoma Gas and Electric and Ameren said 200 000 customers at one point were without power in Oklahoma, Missouri and Illinois.