Rescue teams combed through pulverized buildings and splintered homes early Tuesday after one of the deadliest tornadoes in U.S. history blasted through Oklahoma City and its suburbs, killing at least 24 people, including eight children.

The confirmed death toll from the Oklahoma medical examiner was lowered from an earlier figure of 51, illustrating the confusion as day broke over the shattered city of Moore. Authorities cautioned that the toll could change again.

In Moore, where police said 19 people had been killed, entire blocks appeared as though they had been razed, and cars were mangled beyond recognition. Piled up where houses once stood were scraps of wood, clothes, glass and metal.

At least 120 people were injured in what President Barack Obama called "one of the most destructive tornadoes in history."

Children were among the many missing after the tornado struck Monday afternoon and delivered a direct hit to two elementary schools. Seven children drowned in a pool of water at Plaza Towers Elementary School, which was all but leveled, officials said. The twister also laid waste to a hospital.

"It's absolutely huge. It's horrific," Gov. Mary Fallin said on NBC's TODAY. "It looked like somebody set off something that destroyed structures. Not blocks, but miles."

The threat was not over: Lightning flashed over rescue and cleanup crews, and forecasters warned that more "large and devastating" tornadoes were possible, with big cities in Texas, Louisiana and Arkansas also at risk.

Terry Watkins of the Department of Emergency Management said 101 people had been found alive by search teams.

The dead included the 19 in Moore and five in southern neighborhoods of Oklahoma City, said Moore police Sgt. Jeremy Lewis. The eight children included the seven at Plaza Towers and one at Briarwood Elementary School, he said.

Children from Plaza Towers told of hearing sirens and running into a hall for cover, some still carrying their math books. A teacher, Rhonda Crosswhite, said she huddled with students in a bathroom stall and draped herself over them for cover as the storm hit.

"One of my little boys, he just kept saying, ‘I love you, I love you, please don't with me, please don't die with me,'" she told TODAY. "But we're OK. And we made it out, and it finally stopped."

She said all her students were accounted for.

Damian Britton, a fourth-grader, credited "Miss Crosswhite" with saving his life. He estimated it took about five minutes for the twister to pass through before the students emerged from cover to survey the damage and check on their classmates.

"It was just a disaster,'' he said. "There was just a bunch of stuff thrown around and the cars were tipped over, and it smelled like gas."

The tornado tore the roof off the elementary school about 3 p.m. local time. It was not clear how many children still were missing. Some students in fourth, fifth and sixth grade were evacuated to a church, but students in lower grades had sheltered in place, KFOR reported. More than two hours after the tornado struck, several children were pulled out alive.

Rescuers walked through mile after mile of obliterated homes on Monday night, listening for voices calling out from the wreckage. At one hospital, 85 patients, including 65 children, were being treated for minor to critical injuries.

"We thought we died because we were inside the cellar door," Ricky Stover said while surveying the devastated remains of his home. "It ripped open the door and just glass and debris started slamming on us, and we thought we were dead, to be honest."

At the city's St. Andrews United Methodist Church, parents listened as the names of surviving children were read out through a bullhorn Monday night, The Associated Press reported. While some families hugged each other as they were reunited, others were left to wait, fearing the worst as the night dragged on.

"As long as we are here ... we are going to hold out hope that we will find survivors," Trooper Betsy Randolph, a spokeswoman for the Oklahoma Highway Patrol, told Reuters.

The twister cut a path similar to a tornado outbreak that ravaged Oklahoma and Kansas on May 3, 1999, killing 46 people and damaging or destroying more than 8,000 homes. Wind in that outbreak was clocked at 318 mph, the fastest ever recorded.

The twister was a mile wide at its base, according to The Weather Channel. A reporter for KFOR said the tornado kicked up a cloud of debris perhaps two miles wide. The National Weather Service initially classified the storm as an EF4, the second-strongest type, with winds of 166 to 200 mph.

Obama declared a major disaster, making federal aid available to people in five counties.

"In an instant, neighborhoods were destroyed, dozens of people lost their lives, many more were injured, and among the victims were young children trying to take shelter in the safest place they knew, their school," he said from the White House. "So our prayers are with the people of Oklahoma today."

Expressions of grief and support came from across the world. Queen Elizabeth II extended her deepest sympathies, and Pope Francis said on Twitter: "I am close to the families of all who died in the Oklahoma tornado, especially those who lost young children. Join me in praying for them." House Speaker John Boehner ordered flags at the Capitol to half-staff.

Relief efforts sprang up. The Red Cross said it was opening a shelter, and the University of Oklahoma opened some of its housing for displaced families. People took to Facebook in hopes that storm victims might reclaim family photos that landed in yards many miles away.

Aerial pictures of the destruction brought to mind Joplin, the Missouri town virtually wiped off the map two years ago when an EF5 tornado killed 158 people and caused $2.8 billion in damage.

Joplin city officials said Monday they were sending a team of 10 officers and three firefighters to Moore to help. "Giving back in whatever way we can," the mayor said on Twitter.

The tornado Monday also came one day after another cluster of storms in Oklahoma that killed two elderly men in the town of Shawnee. Tens of millions of people from Texas to the Great Lakes — an area covering 55 million people — had been warned to brace for the severe weather.