Children from two Oklahoma schools levelled Monday by a powerful tornado are recounting what it was like to survive the "loud" and "scary" twister, while rescuers near the end of their search for any other remaining survivors or bodies.

"It was just really loud. It was just one boom after another," eight-year-old Mason told CBC's As It Happens.

Mason is in Grade 2 at Briarwood Elementary School — one of two schools directly hit by Monday's tornado.

Mason's teacher placed him under the sink in one of the school's bathrooms. At first, Mason said, he thought it was a typical tornado drill.

"Next thing I know, it strikes my classroom and everything flies everywhere," he said. "The roof fell on top of me."

After the tornado passed, Mason said all that remained of his classroom was its door.

Darrell MacDonald, Mason's dad, arrived at the school shortly after and reunited with his son, whom he said looked stunned. Mason said he hugged his dad, after worrying if his father had survived the tornado.

Search for survivors nears end

Briarwood reported no deaths, while seven students are believed to have died at the second school, Plaza Towers Elementary School in Moore, Okla.

"The roof collapsed on top of them, and [officials] suspect the water lines broke and the children drowned because they couldn’t get up from the debris," rescue worker Becky Nelson told CBC News.

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A woman carries a child through a field near the collapsed Plaza Towers Elementary School in Moore, Okla. (Sue Ogrocki/Associated Press)

The search for survivors and bodies is almost over in Moore.

Fire Chief Gary Bird said Tuesday that he is "98 per cent sure" there are no more survivors or bodies to recover under the rubble in Moore now that every damaged home has been searched at least once. Bird wants each location to be searched three times by nightfall, though heavy rains have slowed efforts and soaked debris piles.

The EF-5 tornado, the most powerful ranking of twister on the enhanced Fujita scale, killed at least 24 people. Bird said no additional survivors or bodies have been found since Monday night.

Canada's Foreign Affairs Minister John Baird issued a statement expressing his condolences on behalf of all Canadians.

"We extend sincere condolences to those who have lost loved ones and wish those injured a speedy recovery," he said.

Students, staff given 16 minutes of warning time

The deadly tornado gave schoolchildren and their teachers a sudden lesson in survival.

At Plaza Towers Elementary School students and staff had about 16 minutes to take shelter before the twister destroyed the building. Sixteen minutes is more warning than area residents are typically told to expect when a twister is on its way, but less than ample when attempting to herd a large number of children.

When the tornado alarm bell rang, "all the teachers started screaming into the room and saying, 'Get into the hallway! We don't want you to die!' and stuff like that," said Grade 6 student Phaedra Dunn. "We just took off running."

Some teachers are said to have thrown themselves over their students, protecting them in corridors and bathrooms from the fury of the storm.

"I tried to hold on to the wall to keep myself safe because I didn’t want to fly away in the tornado," said one young boy.

"We could hear every bit of it. It was scary," added an unidentified young girl. "After [the tornado] went past, I could see the debris flying over, and it sounded like a train."

America's deadliest tornadoes

Since 1900, the five deadliest tornadoes in the U.S. have resulted in:

  • 695 deaths on March 18, 1925, in Missouri, Illinois and Indiana.
  • 216 deaths on April 5, 1936, in Tupelo, Miss.
  • 203 deaths on April 6, 1936, in Gainesville, Ga.
  • 181 deaths on April 9, 1947, in Woodward, Okla.
  • 158 deaths on May 22, 2011, in Joplin, Mo.

The storm ripped off the school's roof, knocked down walls and turned the playground into a mass of twisted plastic and metal as students and teachers huddled in hallways and bathrooms.

Rescue workers passed the survivors down a human chain of parents and neighbourhood volunteers. Parents carried children in their arms to a triage centre in the parking lot. Some students looked dazed, others terrified.

"They literally were lifting walls up and kids were coming out," Oklahoma State Police Sgt. Jeremy Lewis said. "They pulled kids out from under cinder blocks without a scratch on  them."

U.S. Representative Tom Cole, who lives in Moore, said Plaza Towers was the most secure and structurally strong building in the area.  

"And so people did the right thing, but if you're in front of an F-4 or an F-5 there is no good thing to do if you're above ground. It's just tragic," he said on MSNBC TV.

Nine-year-old Ja'Nae Hornsby is believed to be one of seven students who died when the tornado ripped through the building.

Her father, Joshua Hornsby, said that by the time he arrived at the school, officals had converted the parking lot into a triage centre. Hornsby waited at the school all night while the National Guard searched for survivors.

The family said they received a call this morning informing them Ja'Nae did not survive the tornado.

There were no reported fatalities at Briarwood Elementary.

School tornado shelters to be reviewed

Oklahoma has reinforced tornado shelters in more than 100 schools across the state, an emergency official said, but neither Briarwood nor Plaza Towers had one.

Albert Ashwood is director of the Oklahoma Department of Emergency Management. He told reporters Tuesday it's up to each jurisdiction to set priorities for which schools get limited funding for safe rooms.

Ashwood said a shelter would not necessarily have saved more lives at the Plaza Towers, where seven children sheltering in above-ground classrooms were killed. He said no disaster mitigation measure is absolute.

He said authorities are going to review which schools have safe rooms and try to get them in more schools across the state.

At Southmoore High School in Moore, about 15 students were in a field house when the tornado hit. Coaches sent them to an interior locker room and made them put on football helmets, and all survived, according to The Oklahoman newspaper.    

With files from CBC's Lyndsay Duncombe, Associated Press and Reuters