Moore, Oklahoma (CNN) — Rescue workers raced against time and darkness Monday night looking for survivors after a powerful tornado blasted an area outside of Oklahoma City, leveling homes and leaving at least 51 people dead.

At least 20 of the dead were children, including at least seven from Plaza Towers Elementary School in Moore, which lay directly in the path of the monster storm’s wall of wind.

Seventy-five students and staff members had been huddled at the school when the tornado hit, CNN affiliate KFOR reported.

As nightfall descended, determined searchers in hard hats dug in the debris for those possibly trapped, but authorities described the work as a recovery, not rescue, effort. Search lights illuminated their efforts.

A father of a third-grader still missing sat quietly on a stool. Tears fell from his face as he waited for news.

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