Rescue workers are near the end of the search for survivors in the Oklahoma City suburb where a rare and powerful tornado claimed 24 lives, injured at least 230 and left dozens missing.
Police said thunderstorms and lightning slowed the rescue effort on Tuesday, but 101 people had been pulled from the debris alive.
After nearly 24 hours of searching, Moore's fire chief said he was confident there were no more bodies or survivors in the rubble.
The Oklahoma medical examiner's office said on Tuesday that nine children were among those confirmed dead.
President Barack Obama had promised earlier to make available all necessary government resources to Oklahoma to help in the rescue and recovery effort.
|Rescuers search for survivors in Oklahoma
"The people of Moore [Oklahoma] should know that their country will remain on the ground, beside them, for as long as it takes," Obama said at the White House.
The US president called the devastation as "one of the most destructive tornados in history", even though he said the extent of the damage was still unknown.
Obama spoke on Tuesday after an Oval Office briefing on the latest developments from his disaster response team and as Federal Emergency Management Agency Director Craig Fugate was heading to Oklahoma.
Moore was strewn with debris and many residents were without power and water in the structures left still standing in the most severe of a series of savage storms to hit the state on Sunday and Monday.
The tornado razed two schools and ripped off the roof of a medical centre.
Scientists concluded the tornado was an EF5 on the enhanced Fujita scale, the most powerful type, capable of lifting reinforced buildings off the ground, hurling cars like missiles and stripping trees completely free of bark. The amount of energy released dwarfed the power of the atomic bomb that levelled Hiroshima.
The tornado covered about 30km of ground as it demolished buildings including Plaza Towers Elementary School where about two dozen children had sought shelter inside from the storm when the building collapsed and trapped them in the rubble.
|Al Jazeera meteorologist Richard Angwin explains how the deadly Oklahoma tornado developed.
At least 45 of the 230 people known to have been injured were children, according to area hospitals.
Families anxiously waited at Moore churches to hear if their loved ones were all right.
A man with a megaphone stood on Monday night near St Andrews United Methodist Church and called out the names of surviving children as parents waited nearby.
Another elementary school, homes and a hospital were among the buildings levelled in Moore.
Obama earlier spoke with Oklahoma Governor Mary Fallin to express his concern and ordered federal aid to help the state and local recovery efforts.
Fallin told reporters that "hearts are broken" for parents looking for their children.
She declared 16 counties disaster areas and deployed the state National Guard and extra police to assist with rescue operations.
More tornadoes possible
The National Weather Service (NWS) predicted a 10 percent chance of more tornadoes in parts of Texas, Oklahoma, Arkansas, Kansas, Missouri and Illinois.
It said parts of four other states - Wisconsin, Indiana, Michigan and Iowa - had a five percent risk of tornadoes.
The area at greatest risk includes Joplin, Missouri, which on Wednesday will mark two years since a massive tornado killed 161 people.
The latest tornado in Oklahoma came as the state was still recovering from a strong storm on Sunday with fist-sized hail and blinding rain.
Two men in their 70s died in the storm, said a spokeswoman for the Oklahoma Office of Emergency Management.
Thirty-nine people were injured around the state as storms toppled trees and tore up rooftops, she said.