Americans who survived a massive tornado that ripped through an Oklahoma City suburb say they raced for shelter only to emerge to find their homes flattened.
Officials say at least 24 people have died, including nine children whose primary school collapsed. At one point 90 people were feared dead.
The powerful 3km-wide tornado carrying winds of up to 320km/h struck at 2.56pm (local time) on Monday and remained on the ground for about 45 minutes.
Worst hit was the suburb of Moore, south of the city, where winds of up to 320km/h whipped through, destroying a school, sparking fires and devastating homes and buildings, the BBC reports.
The Oklahoma chief medical examiner's office said nine children were among those confirmed dead.
Plaza Towers Elementary school took a direct hit: the storm tore off the building's roof and knocked down walls.
Another school - Briarwood Elementary - was also damaged, and teachers were later seen leading pupils out to safety.
Oklahoma's Lieutenant Governor Todd Lamb said the tornado may have been the most powerful ever to hit the United States.
"If you could imagine a lawnmower blade that was two-and-a-half miles wide just being lowered on a community and the havoc that that would wreak ... churches have been destroyed, neighbourhoods obliterated, schools flattened, hospitals hit and loss of life."
Colt Forney is a meteorologist who chases tornadoes in the American mid-west. He told Radio New Zealand's Checkpoint programme he and three others were sitting in their SUV in a car park as the tornado passed less than 1km away.
"You could see pieces of house being lofted in the air. I remember seeing what appeared to be an entire roof of a house get carried halfway around the tornado. There was debris everywhere in the air."
Those who actually experienced the twister say they are lucky to be alive and described the sound like a freight train coming through.
President Barack Obama has declared a major disaster in Oklahoma and ordered federal authorities to join in the search efforts which are continuing throughout the night. Rescuers are using flood lights and sniffer dogs in a desperate search for survivors.
Oklahoma Governor Mary Fallin said it was a "tragic" day.
The storm has been given a preliminary classification of EF-4 on the enhanced Fujita scale.
Second day of storms
It is the second day in a row that the state of Oklahoma has been slammed by twisters. On Sunday, at least two people died and 21 were injured by tornadoes.
A trailer park near the town near the town of Shawnee, 55km from Oklahoma City, is said to have been razed.
Two men, aged 76 and 79, were killed near the mobile home park on Highway 102, Oklahoma's state medical examiner confirmed. Both lived in Shawnee, but it was not immediately clear whether either or both lived in mobile home park.
The governor of Oklahoma, Mary Fallin, says a state of emergency has been declared in 16 counties to enable help to get to the worst-hit parts of the state.
At least four tornadoes ravaged the state on Sunday, part of a storm system that was moving north-east across the Midwestern states and Texas. Tornadoes, hail and high winds also hit Iowa and Kansas.