The 2-mile (3-km) wide tornado tore through the town of Moore outside Oklahoma City, trapping victims beneath the rubble as one elementary school took a direct hit and another was destroyed. Plaza Towers Elementary School sustained a direct hit and television pictures showed firefighters from more than a dozen fire departments working under bright spotlights to find survivors. President Barack Obama declared a major disaster area in Oklahoma, ordering federal aid to supplement state and local efforts in Moore after the deadliest U.S. tornado since one killed 161 people in Joplin, Missouri, two years ago.

There was an outpouring of grief on Plaza Towers' Facebook page, with messages from around the country including one pleading simply: "Please find those little children." A separate Facebook page set up to reunite people in the area hit by a tornado on Sunday with their belongings and pets also showed entries for Moore residents overnight. Another elementary school, homes and a hospital were among the buildings leveled in Moore, leaving residents of the town of about 50,000 people stunned at the devastation and loss of life. Many residents were left without power and water.

The Oklahoma medical examiner said 20 of the 91 expected to have been killed were children. The office had already confirmed 51 dead and had been told during the night by emergency services to expect 40 more bodies found in the debris, but had not yet received them. At least 60 of the 240 people injured were children, area hospitals said.

The National Weather Service assigned the twister a preliminary ranking of EF4 on the Enhanced Fujita Scale, meaning the second most powerful category of tornado with winds up to 200 mph. Moore was devastated with debris everywhere, street signs gone, lights out, houses destroyed and vehicles tossed about as if they were toys. The dangerous storm system threatened several southern Plains states with more twisters. The area around Moore faces the risk of severe thunderstorms on Tuesday, which could hamper rescue efforts.

SCHOOL DESTROYED

The National Weather Service Storm Prediction Center provided the town with a warning 16 minutes before the tornado touched down at 3:01 p.m., which is greater than the average eight to 10 minutes of warning, said Keli Pirtle, a spokeswoman for the center in Norman, Oklahoma. The notice was upgraded to emergency warning with "heightened language" at 2:56 p.m., or five minutes before the tornado touched down, Pirtle said.

Television media measured the tornado at more than 2 miles wide, with images showing entire neighborhoods flattened. The U.S. Federal Aviation Administration (FAA) imposed a temporary flight restriction that allowed only relief aircraft in the area, saying it was at the request of police who needed quiet to search for buried survivors. Oklahoma activated the National Guard, and the U.S. Federal Emergency Management Agency activated teams to support recovery operations and coordinate responses for multiple agencies.

Briarwood Elementary School, which also stood in the storm's path, was all but destroyed. On the first floor, sections of walls had been peeled away, giving clear views into the building; while in other areas, cars hurled by the storm winds were lodged in the walls. The massive twister struck at the height of tornado season, and more were forecast. On Sunday, tornadoes killed two people and injured 39 in Oklahoma.