Authorities say an elementary school in the Oklahoma City suburb of Moore took a direct hit from a mile-wide tornado.
The death toll has risen to 51 people, according to CNN.
Local television reported Plaza Towers Elementary suffered "extensive damage" on Monday afternoon. Witnesses said there were at least 75 people inside the school when the tornado hit.
Neighborhoods are flattened and blown apart, with shards of wood and pieces of insulation strewn everywhere. Television footage also showed first responders picking through rubble and twisted metal in the suburb south of Oklahoma City.
The suburb of Moore was hit hard by a tornado in 1999. The storm had the highest winds ever recorded near the earth's surface.