U.S. President Barack Obama has pledged urgent government help for the victims of a massive tornado that smashed through a town in the south-central U.S. state of Oklahoma.
Obama, in a statement at the White House, described the storm as one of the "most destructive tornadoes in history," although the full scale of the devastation is not yet known.
Authorities say at least 24 people were killed after the storm hit the town of Moore, a suburb of Oklahoma City, on May 20.
The Medical Examiner's Office says a previous toll of 51 dead may have included double-reporting of casualties.
Some of those killed were children under 12, caught in an elementary school by the twister.
Obama has declared a major disaster in the area.
The U.S. National Weather Service said the tornado had wind speeds of up to 320 kilometers per hour and had a preliminary ranking of EF4 on the Enhanced Fujita Scale, meaning the second most powerful category of tornado.
One survivor, Ricky Stover, said the force of the storm was so strong that it unlatched cellar doors where residents sought shelter.
"You see the latch coming undone and we couldn't reach for it and it ripped open the door and just glass and debris started slamming on us," Stover said. "We thought we were dead, to be honest."
The National Weather Service Storm Prediction Center had issued a warning to Moore just 16 minutes before the tornado touched down at around 3 p.m. local time.
The White House said that under Obama's declaration of a major disaster, individuals and business owners affected by the tornado may apply for federal grants for temporary housing and home repairs, low-cost loans to cover uninsured property losses, and other programs.
The tornado loosely followed the path of a twister that hit the same region in May 1999. That tornado destroyed or damaged more than 8,000 homes, killing at least two people.
With reporting by AP and Reuters