(MOORE, Okla.) -- First responders are in a race against time in the search for any survivors of a devastating tornado that ripped through Moore, Okla., while the medical examiner's office has revised the death toll from 51 to 24, including nine children.
Oklahoma medical examiner spokeswoman Amy Elliot said Tuesday morning that she believes some victims were counted twice in the early chaos of the storm. The original death toll included 20 children.
Two elementary schools were in the path of Monday's tornado, which the National Weather Service gave a preliminary rating of at least EF-4, meaning churning wind speeds of up to 200 mph.
Oklahoma City police spokesman Sgt. Gary Knight said seven of the young victims were from Plaza Towers Elementary School.
Moore Mayor Glenn Lewis and National Guard members told ABC News the search-and-rescue operation at the school is now a body-recovery effort.
"The walls were just pancaked, absolutely flattened and the students were just grouped together," Lt. Gov. Todd Lamb told ABC News.
Oklahoma Gov. Mary Fallin tweeted late Monday night that she visited with search crews at the elementary school. "Appreciate their hard work and tireless dedication," she tweeted.
Fallin has also deployed 80 National Guard members to help with search-and-rescue efforts throughout the city.
Authorities said Briarwood Elementary School in Moore received a "direct hit" from the storm and was also destroyed, with its roof and walls blown off.
A total of 242 patients, including 58 children, were treated at hospitals. Many patients have been treated and discharged while others have been transferred among hospitals.
Kelly Wells, spokeswoman for Norman Regional Health System, which oversees three hospitals in Oklahoma, said lacerations, broken bones, head and neck injuries were the most common.
Moore Medical Center, the only hospital in Moore, sustained major damage and was evacuating all its patients to other hospitals.
Betsy Randolph of the State Highway Patrol asked people not involved in search-and-rescue operations to stay off the roads so first responders can do their job.
President Obama signed a disaster declaration in Oklahoma and ordered federal aid to supplement state and local recovery efforts in the area affected by severe storms and tornadoes.
The first tornado warning went out around 2:40 p.m. local time and just 16 minutes later a tornado tore a 12-mile gash in Oklahoma from Newcastle to Oklahoma City. Frantic groups of rescuers could be seen digging through debris within minutes after the tornado blew by.
Moore, a community of 41,000 people about 10 miles south of Oklahoma City, saw homes wiped off their foundations and cars tossed like toys on top of nearby buildings. Block after block lay in ruins, reduced to smoking piles of wood and brick.
The weather service estimated that the tornado was at least a half-mile wide and says it could have been on the ground for as long as 40 minutes.
As Moore continues to sift through rubble for survivors, millions across the Midwest are once again under the threat of tornadoes. People in northeast Texas all the way to southwest Arkansas have a 10 percent chance of seeing a twister later Tuesday.
Millions of people from San Antonio, Texas, all the way to Michigan could see damaging hail and even a chance of isolated tornadoes.
More than 50 tornadoes ravaged the Midwest this weekend, killing a 79-year-old man in Shawnee, Okla.
Monday's devastation in Oklahoma came almost exactly two years after an enormous twister ripped through the city of Joplin, Mo., killing 158 people and injuring hundreds more.
Moore was the site of one of the most destructive tornadoes in U.S. history. An EF-5 tornado ripped through the Oklahoma City-area May 3, 1999, killing 42 people.
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