MOORE, Oklahoma (AFP) - US President Barack Obama offered solace and support to residents of Oklahoma on Sunday as they rebuild their shattered lives after a monster tornado killed 24 people.

"When we say that we've got your back, I promise you that we keep our word," Mr Obama declared, as he stood in front of the wreckage of Plaza Towers Elementary School.

In the shadow of the now unrecognisable mountain of twisted metal and wood where many of the storm's 10 child victims lost their lives, he praised all those who went out of their way to save people's lives.

"From the forecasters who issued the warnings, to the first responders who dug through the rubble, to the teachers who shielded with their own bodies their students, Oklahomans have inspired us with their love and their courage and their fellowship," Mr Obama said.

He also hailed those who have offered shelter for their neighbours whose homes were destroyed.

"This is a strong community with strong character. There's no doubt they're going to bounce back. But they need help," he said.

"Just like any of us would need help if we saw the kind of devastation that we're seeing here." Mr Obama was in Oklahoma to view the devastation firsthand and meet with survivors and first responders. He was accompanied through the scene by Governor Mary Fallin, Federal Emergency Management Agency (FEMA) Administrator Craig Fugate and local officials.

At a firehouse later in the day, where various agencies were offering aid, Mr Obama praised the "great" work and coordination that saved "so many" lives.

The tornado was one of the most powerful in years, injuring 377 people, damaging or destroying 1,200 homes and affecting an estimated 33,000 people, according to a recent update from officials.

Initial damages have been estimated at around US$2 billion (S$2.5 billion).

Speaking to CNN earlier in the day, Ms Fallin said she was seeking help streamlining assistance to her battered state from FEMA.

"What I need is the ability to get through red tape, the ability to get the FEMA funds in here quickly and to get the services that our citizens need to help them recover through this terrible disaster," she said.

"The debris, as you can see behind me, is huge. It's not just a couple houses with roofs off.

"This is a massive debris field. It's not just a couple blocks. It's miles. It's 27km long, almost 2.4km wide." The town of Moore suffered a similarly powerful tornado in 1999 that killed 41, and another in 2003.

A public memorial was scheduled to take place later in the day.

But Fallin emphasized the tight-knit community was also rallying together to move on.

"We're resilient. There's already a big path of debris that's been moved around. People are gathering their stuff," she said.

Part of that process has included taking up the threads of ordinary life, including holding scheduled graduations.

Three area high schools held ceremonies on Saturday back-to-back at a local convention center.

Free caps and gowns were distributed to students who had lost their homes in the tornado.

The United States experiences three out of four tornadoes in the world, but the one that hit Monday was an unusually powerful EF-5 - the highest possible level - on the Enhanced Fujita scale and touched down with little advance notice.

It followed roughly the same track as the 1999 twister, yet very few homes in Oklahoma - and neither of the stricken schools - had purpose-built storm shelters.