[Updated at 6:10 p.m. CT]

MOORE, Okla. — Scientists surveying the aftermath here Tuesday deemed the tornado to be the worst of the worst, saying its winds were at least 200 mph and possibly stronger. Some victims didn't have long to react.

“The storm intensified very rapidly in four miles or around 10 minutes,” the National Weather Service revealed in a preliminary report.

The tornado cut a path of destruction 17 miles long and 1.3 miles wide.

Kelly Damphousse was one of those caught off guard. He and his family were unloading a 26-foot U-Haul truck at a storage facility when they spotted the ferocious funnel.

“It just kept coming,” said Damphousse, who was able to flee the twister's path.

Twenty-four people have been confirmed dead—including 9 children—and 237 were injured by the tornado, Oklahoma Gov. Mary Fallin said. At a news conference Tuesday, Fallin said officials are trying to find out if other victims might have been taken to local funeral homes and have not yet been counted in the death toll.

“We're going through that debris, and we're going to keep looking until everybody's found,” FEMA Administrator Craig Fugate said at the news conference. Dozens of people have been rescued.

Fallin said authorities "don't even know if there are missing people" but will turn over every piece of debris to find survivors possibly trapped in the rubble. First responders will check each damaged piece of property three times to ensure no one who needs help is overlooked, Fallin said.

“This was the storm of storms,” Oklahoma City Mayor Mick Cornett said.

[Photos from the scene.]

Earlier, authorities said they expected more victims to be uncovered.

“Not to be pessimistic ... but we think the death toll will continue to climb as we find more bodies,” Lt. Gov. Todd Lamb said on CNN.

Mother Nature was showing no mercy to Moore on Tuesday. Drenching rains, lightning and marble-size hail slowed rescuers at times on Tuesday.

Officials said water, electricity and cell phone service was down in some areas. They urged people to stay away from the area. Residents can call 1-800-621-FEMA to find shelter.

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President Barack Obama said the federal government would help with the disaster response.

“The people of Moore should know that their country will remain on the ground there for them, beside them, as long as it takes for their homes and schools to rebuild, businesses and hospitals to reopen, the parents to console, the first responders to comfort and of course frightened children who will need our continued love and attention,” Obama said Tuesday morning at the White House.

[Residents’ storm stories: ‘We can’t go back, the destruction is so bad’]

Seven of the dead children were found Monday night at Plaza Towers Elementary School, which took a direct hit when the tornado chewed its destructive path through Newcastle, Moore and parts of southern Oklahoma City for 50 minutes. Officials said that unlike 100 other schools in the area, Plaza Towers was not equipped with a tornado safe room.

Schools Superintendent Susan Pierce choked up at a news conference when talking about the twister, which destroyed at least two schools. She said every Moore school implemented its tornado shelter plan before the storm hit Monday. "We're in the process of learning as much as we can about what happened," she said, adding that graduation for Moore's high school seniors will still take place this Saturday in Oklahoma City.

Classes were still in session at Plaza Towers when the twister crushed nearly every corner of the property. Teachers’ cars were thrown into the building, and the playground no longer exists.

“All you could hear were screams,” local resident Stuart Earnest Jr. said of the scene at the school after the storm. “The people screaming for help. And the people trying to help were also screaming.”

“I can only hope those little kids killed didn't suffer,” said Earnest, one of many who rushed to the school to help survivors.

[In tornado's wake, worried parents seek out kids]

With several students still unaccounted for, rescuers worked overnight digging through the rubble. Police say they are still digging through the structure.

“I just hope they find her,” Shannon Galarneau said of her 10-year-old niece, a Plaza Towers student who was missing as of early Tuesday morning. “You just feel helpless.”

The girl's younger sister, also a student at the school, survived but suffered cuts to her head and bruises on her back. The 8-year-old was still wearing her hospital bracelet while asleep on her grandmother's shoulder in the front seat of a pickup truck just after midnight.

“She said it was probably the scariest day of her life,” Galarneau said.

Monday's tornado was estimated to be more than a mile wide at times. Its path was nearly identical to the one taken by a record-breaking May 1999 tornado that devastated the area.

Galarneau and her husband could see the twister a mile and a half from their front porch and scrambled to hide.

“It barreled down fast,” said Galarneau, who found refuge in a utility closet.

[How to Help: Oklahoma storms]

Obama declared several Oklahoma counties disaster areas and pledged to support the area's rescue and recovery. The funnel’s fury crumbled homes for several blocks around the school and in other parts of Moore. Missing street signs and other landmarks made some neighborhoods unrecognizable even to locals.

“It is a barren wasteland,” Galarneau said. “Everything is leveled.”

Allen and JoAnn Anderson huddled under quilts and pillows in their bathtub with their Yorkie, Magand, and cat, Meow, when the tornado came down their street.

“It was like standing in the middle of a train track and having the train go right over you,” said Allen, 63.

They emerged from the tub 15 minutes later to find their brick house gone and cars badly damaged.

“There’s no house. It’s just a pile of rubble,” Allen said.

The couple checked into a motel with their pets late Monday. Chunks of attic insulation were still stuck in JoAnn’s sandy-blond hair, and her legs were partially caked in dried mud.

“It could be worse,” JoAnn said. “We're alive.”

The official count of people treated at local hospitals doesn't include unreported cases of minor injuries or the untold emotional toll.

A CVS drugstore not far from Plaza Towers elementary was averaging three to four patients an hour on Tuesday, according to Carrie Geurts, a nurse practitioner there.

“Don't endanger yourself,” said Geurts, whose MinuteClinic staff had seen patients for scrapes, a gashed leg and possible cases of PTSD.

She said a handful of civilians who had spent the night looking for casualties, “are just glad to get in here and talk.”

“People need to remember to take care of themselves too,” Geurts said.

--Yahoo News' Liz Goodwin is reporting from New York.