US rescuers search for tornado survivors
The Oklahoma medical examiner's office said on Tuesday that 20 children were among those confirmed dead and the death toll was expected to rise.
President Barack Obama has promised to make available all necessary government resources to Oklahoma to help in the rescue and recovery effort.
"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.
Oklahoma City Police Department Lieutenant Kevin Parton said rescuers were searching for victims as police and National Guard secured the disaster scene and conducted patrols at the centre of the devastation in Moore, a community of about 50,000 people to the south of Oklahoma City.
"There's still emergency workers inside that are doing recovery efforts of the bodies of the victims," Parton said.
"We're always hopeful that we'll find someone still alive inside the rubble but being realistic I would say probably not."
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.
School collapsed
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.
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 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.
Aljazeera
