A tornado of rare power, that may be among the largest and most destructive in US history, has roared through an Oklahoma City suburb, killing at least 51 people, flattening neighbourhoods with winds up to 200mph and destroying at least one school.
Officials said children from the school were among the dead and the overall death toll was expected to rise, an Oklahoma Medical Examiner's Office spokeswoman said.
Rescuers combed through the debris as darkness fell and rain began to fall. More than 140 people were being treated at hospitals, including about 70 children, some in a critical condition.
"Hearts are broken" for parents looking for their children, governor Mary Fallin said.
The ferocious storm - less than 1% of all tornadoes reach such wind speed - ripped through the suburb of Moore in a Midwest region of the US known as Tornado Alley. Street after street lay in ruins and cars and trucks were left crumpled.
The National Weather Service estimated that the tornado reached up to half a mile wide and was an EF-4 on the enhanced five-point Fujita scale, the second most powerful type of twister.
In video footage, the dark funnel cloud moved slowly across the landscape for more than half an hour, scattering shards of wood, pieces of insulation, shingles and glass over the streets.
The focus quickly turned to Plaza Towers Elementary School, where the storm tore off the roof, knocked down walls and turned the playground into a mass of twisted plastic and metal.
"You could see the debris, like pieces of shingles and insulation and stuff like that, rotating around it," said Chris Calvert, who saw the tornado from about a mile away.
Several children were pulled alive from the rubble. Rescue workers passed them down a human chain to a triage centre in the car park.
As night fell, emergency workers crawled through the ruins, looking for people. Crews used jackhammers and sledgehammers to tear away concrete. Bulldozers were getting stuck in the mud.
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 put in the restroom.
After the tornado passed, Tiffany Thronesberry said she got a panicked call from her mother, Barbara Jarrell.
"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 with cuts and bruises.
Dangers remained. Downed power lines and open gas lines posed a risk, police captain Dexter Nelson said. Television footage showed at least one fire in the debris.
The same suburb was hit hard by a tornado in 1999. That storm produced the highest winds ever recorded near the Earth's surface - 302mph.
"Oklahoma City has had more tornado strikes than any other city in the United States," the city government's website says.
President Barack Obama called Ms Fallin to express his concern.
Are you in the area? Have you been affected by the tornadoes?
10 deadliest tornadoes in US 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.
How to help
In the United States the Oklahoma Red Cross is asking people to donate by texting Red Cross to 90999 – that counts for a $10 donation. The organisation has a number of shelters open for those displaced by the storm.
You can also donate to the Salvation Army, if in the United States, by phone: 800-725-2769 -- or online at: donate.salvationarmyusa.org