The preliminary rating of a tornado in Moore, Oklahoma, is at least EF-4 (166 to 200 mph winds), the National Weather Service said.
"People are trapped. You are going to see the devastation for days to come," Betsy Randolph, spokeswoman for Oklahoma Highway Patrol, told CNN.
Interstate 35 in Moore was closed as a result of debris from the tornado. Moore Medical Center was evacuated after sustaining damage, a hospital spokeswoman said.
Follow complete coverage of the storm on CNN TV, http://cnn.com and CNN Mobile.
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