The state medical examiner's office confirmed that the death toll had risen to at least nine, including at least two children, according to local media report.
The Oklahoma State Department of Health reported that Oklahoma City-area hospitals treated 104 people. More than half of those were people who had been cut or pierced.
According to the Oklahoma Highway Patrol Trooper Betsy Randolph, a woman and her child were killed when their SUV overturned on the state highway as an enormous tornado swept through the area yesterday.
"We try to tell people not to drive into the storm," Oklahoma Highway Patrol Trooper Betsy Randolph said.
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"And this may have been one of those deals where there was little or no notice or warning. It's just so gut-wrenching and it's so heartbreaking," she said.
The accident happened as an enormous tornado swept through the area yesterday. The tornado was part of a midwestern storm system that spun off twisters as far away as St Louis, Missouri.
More than 200,000 customers were without power in Oklahoma, Missouri and Illinois area because of the severe weather, the Oklahoma Gas and Electric Company said.
Heavy rain was forecast for tomorrow, which could hinder rescue and recovery efforts further.
"The flooding is the major problem in the Oklahoma City metro," Lt. Jay Barnett of the Oklahoma City Police Department told The Oklahoman. "A lot of that has to do with people who, for whatever reason, instead of sheltering decided to outrun the storm and got caught in it."
"Areas of the city that don't normally flood - we're seeing flooding," he said.
High winds were forecast for Moore, the suburb where a monster tornado had killed 24 people, including 10 children on May 20.