As the search for survivors comes to a close in an Oklahoma City suburb ravaged by a monstrous EF-5 tornado that killed 24 people, harrowing accounts of the storm’s wrath are emerging.

Chelsie McCumber, a resident of Moore, said she grabbed her two-year-old son, Ethan, and covered him with a mattress before taking shelter in the coat closet of her home.

“I told him we’re going to play tent in the closet,” McCumber said.

She sang to her son when he complained it was getting warm inside the cramped space. “Time just kind of stood still,” recalled McCumber. “I was kind of holding my breath, thinking this isn’t the worst of it yet.”

When the pair emerged from the closet, McCumber said she was shocked by the devastation left by the mammoth storm. “When I got out, it was worse than I thought.”

On Tuesday, the National Weather Service confirmed it was an EF-5 twister, the fiercest and most destructive possible.

Keli Peritle, a spokesperson for the weather agency, said the tornado was upgraded from an EF-4 to an EF-5 based on the damage an assessment team saw on the ground.

The national weather agency described the twister, which had a path of destruction of 27 kilometres long and two kilometres wide, as “incredible.” Winds were clocked at more than 322 km/h, and authorities said that less than one per cent of all tornadoes reach such speeds.

The Enhanced Fujita scale, or EF scale, is the standard for rating tornadoes’ strength. It is based largely on wind speed and degrees of damage to structures, such as apartment buildings, schools and shopping malls, and vegetation, such as trees.

An EF-1 tornado has wind speeds of up to 137 km/h. EF-5 twisters have wind speeds exceeding 322 km/h.

Authorities on Tuesday said 24 people, including nine children, were killed when the twister ripped through the small town in a central U.S. region known as Tornado Alley. Homes were reduced to piles of splintered wood, and a local elementary school was demolished.

“We will rebuild and we will regain our strength,” Gov. Mary Fallin said. Fallin, who went on a flyover of the area, said the destruction was “hard to look at.”

An aerial view of the town shows large patches of turned-over red dirt where the tornado, which was on the ground for 40 minutes, had ripped through the town. Squares of concrete slabs could be seen where homes once stood and a pond was filled with piles of wood.

Authorities say they have yet to determine the full scope of damage left by the tornado and they do not know the number of families that have been displaced.

A fresh crew of emergency workers moved in on Tuesday to continue the search-and-rescue effort undertaken by more than 200 personnel overnight. By Tuesday evening, after nearly 24 hours of searching, the town’s fire chief said he was confident there were no more bodies or survivors left.

“I’m 98 per cent sure we’re good,” Fire Chief Gary Bird said at a press conference. He said crews have combed through every damaged home at least once.

Bird said his goal was to search each building three times just to be certain there were no more bodies or survivors. He said he expects the search for survivors to come to a close Tuesday night, though heavy rains have dampened their efforts.

Emergency crews have also run into difficulty navigating the devastated neighbourhoods as no street signs or recognizable landmarks are left. Some rescue workers relied on smartphones or GPS devices to guide them.

The death toll was initially reported to be 51 but was lowered. In the early chaos after the storm some victims were counted twice, Amy Elliot, a spokesperson for the state’s medical examiner’s office, told The Associated Press.

More than 200 people have been treated at surrounding hospitals.

Meanwhile, in Washington, President Barack Obama pledged government help for the community of 56,000 people 26 km south of Oklahoma City.

"In an instant, neighbourhoods were destroyed, dozens of people lost their lives, many more were injured," Obama said. "Among the victims were young children trying to take shelter in the safest place they knew -- their school."

Early Tuesday morning, rescue teams at Plaza Towers Elementary were able to pull several students from under a collapsed wall. Some students looked confused, others scared as workers passed the survivors down to parents and volunteers. Seven of the nine dead children were killed at that school.

The twister tore off the school’s roof and destroyed the playground, leaving behind a heap of twisted metal and plastic. Moments before the twister destroyed the elementary school, the tornado alarm sounded, recalled sixth-grader Phaedra Dunn.

“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,” Dunn said. “We just took off running.”

While more than 100 schools across Oklahoma have reinforced tornado shelters, Plaza Towers Elementary and nearby Briarwood Elementary did not.

Messages of condolence have poured in to the community from around the world, including from UN Secretary-General Ban Ki-moon, who offered the assistance of the United Nations, according to deputy spokesperson Eduardo del Buey.

With files from The Associated Press