A monstrous tornado at least a half a mile wide roared through the Oklahoma City suburbs, flattening neighbourhoods and destroying a school as children and teachers huddled against winds up to 200mph.
At least 51 people were killed, including at least 20 children, and officials said the death toll was expected to rise.
The storm laid waste to scores of buildings in Moore, a community of 41,000 people about 10 miles south of Oklahoma City. Street after street lay in ruins, homes were crushed into piles of broken wood and cars and trucks were left crumpled on the roadside.
The National Weather Service issued an initial finding that the tornado was an EF-4 on the enhanced Fujita scale, the second most-powerful type of twister.
More than 120 people were being treated at hospitals, including about 50 children. Search-and-rescue efforts were continuing through the early hours.
Tiffany Thronesberry said she heard from her mother, Barbara Jarrell, shortly after the tornado.
“I got a phone call from her screaming, ’Help! Help! I can’t breathe. My house is on top of me!”’ Ms Thronesberry said.
She hurried to her mother’s house, where first responders had already pulled her out. Her mother was treated in hospital for cuts and bruises.
Oklahoma governor Mary Fallin deployed 80 National Guard members to helpt with rescue operations and extra highway patrol officers.
She also spoke to President Barack Obama, who declared a major disaster and ordered government aid to supplement state and local recovery efforts.
Many landlines to stricken areas were down, and mobile phone networks congested.
In a video of the storm, the dark funnel cloud could be seen marching slowly across the green landscape. As it churned through the community, the twister scattered shards of wood, awnings and glass all over the streets.
The tornado also destroyed the community hospital and some stores. Moore’s mayor Glenn Lewis watched it pass through from his jewellery shop.
“All of my employees were in the vault,” he said.
Chris Calvert saw the menacing tornado from about a mile away.
“I was close enough to hear it,” he said. “It was just a low roar, and you could see the debris, like pieces of shingles and insulation and stuff like that, rotating around it.”
Even though his sub-division is a mile from the tornado’s path, it was still covered with debris. He found a picture of a small girl on Santa Claus’ lap in his yard.
Volunteers and first responders raced to search the debris for survivors.
At Plaza Towers Elementary School, the storm tore off the roof, knocked down walls and turned the playground into a mass of twisted plastic and metal.
Children from the school were among the dead, but several were pulled alive from the rubble. Rescue workers passed the survivors down a human chain to the triage centre in the car park.
James Rushing, who lives opposite, heard reports of the approaching tornado and believing he would be safer there, ran to the school, where his five-year-old foster son Aiden is a pupil.
“About two minutes after I got there, the school started coming apart,” he said.
The pupils were sent into the restroom.
A man with a megaphone stood near a Catholic church and called out the names of surviving children as parents waited nearby, hoping to hear their sons’ and daughters’ names.
As dusk began to fall, heavy equipment was rolled up to the school, and emergency workers wearing yellow crawled among the ruins, searching for survivors.
Because the ground was muddy, bulldozers and front-end loaders were getting stuck. Crews used jackhammers and sledgehammers to tear away concrete, and chunks were being thrown to the side as the workers dug.
A map provided by the National Weather Service showed that the storm began yesterday west of Newcastle and crossed the Canadian River into Oklahoma City’s rural far south-western side about 3pm local time. When it reached Moore, the twister cut a path through the centre of town before lifting back into the sky at Lake Stanley Draper.
Captain Dexter Nelson of Oklahoma City Police said downed power lines and open gas lines posed a risk in the aftermath of the system.
The weather service estimated that the tornado was at least half a mile wide. The 1999 storm had winds clocked at 300 mph.
Kelsey Angle, a weather service meteorologist in Kansas City, Missouri, said was unusual for two such powerful tornadoes to track roughly the same path.
It was the fourth tornado to hit Moore since 1998. A twister also struck in 2003.
Don Denton had not heard from his two sons since the tornado hit the town, but the man who had endured six back surgeries and has a severe limp said he walked about two miles as he searched for them.
As reports of the storm came in, Mr Denton’s 16-year-old son texted him, telling him to call.
“I was trying to call him, and I couldn’t get through,” he said. Eventually,his sons spotted him in the crowd, fine, but upset to hear that their grandparents’ home was destroyed.
DEADLIEST U.S. TORNADOES SINCE 1900
Here is a list of the 10 deadliest tornadoes in the United States since 1900.
:: 695 deaths. March 18, 1925, in Missouri, Illinois and Indiana.
:: 216 deaths. April 5, 1936, in Tupelo, Mississippi.
:: 203 deaths. April 6, 1936, in Gainesville, Georgia.
:: 181 deaths. April 9, 1947, in Woodward, Oklahoma.
:: 158 deaths. May 22, 2011, in Joplin, Missouri.
:: 143 deaths. April 24, 1908, in Amite, Louisiana, and Purvis, Mississippi.
:: 116 deaths. June 8, 1953, in Flint, Michigan.
:: 114 deaths. May 11, 1953 in Waco, Texas.
:: 114 deaths. May 18, 1902 in Goliad, Texas.
:: 103 deaths. March 23, 1913, in Omaha, Nebraska.
Source: National Oceanic and Atmospheric Administration.