Xclusive: Vast Oklahoma Tornado Kills at Least 91 People [FULL STORY]

Clinging to the hope of finding more survivors, rescue workers raced overnight scouring mountains of rubble where houses and schools once stood-- even as the sobering death toll continued to climb.

The vicious tornado that tore across central Oklahoma on Monday has killed at least 51 people -- with about 40 more bodies expected to arrive at the Oklahoma Medical Examiner's office, Amy Elliott of the coroner's office said. The official death toll will gradually rise as the bodies are processed.

Tornado leaves path of destruction

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Rescue efforts continue at school

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At least 20 of those killed were children, including seven from Plaza Towers Elementary School in Moore -- the site of a frantic search early Tuesday morning. About 75 students and staff members hunkered down in the school when the tornado hit, CNN affiliate KFOR reported. The school in the direct path of the monster storm's fury. A father of a third-grader still missing sat on a stool outside. Tears cascaded from his face as he waited quietly for any news. Even parents of survivors couldn't wrap their minds around the tragedy.

"I'm speechless. How did this happen? Why did this happen?" Norma Bautista asked. "How do we explain this to the kids? ... In an instant, everything's gone." Across Moore, even the city's main hospital fell victim to the tornado. "Our hospital has been devastated," Mayor Glenn Lewis said. "We had a two-story hospital, now we have a one. And it's not occupiable." So dozens of wounded had to be rushed to other hospitals.

At least 145 people were taken to three area hospitals. That number includes 45 children taken to the children's hospital at Oklahoma University Medical Center, Dr. Roxie Albrecht said. Injuries ranged from minor to severe, including impalement and crushing injuries.