The National Weather Service says the tornado that hit Moore, Okla., was a top-of-the-scale EF-5 twister with winds of at least 200 mph.
Spokeswoman Keli Pirtle said Tuesday the agency upgraded the tornado from an EF-4 on the enhanced Fujita scale to an EF-5 based on what a damage assessment team saw on the ground. The weather service uses the word "incredible" to describe the power of EF-5 storms.
The weather service says the tornado's path was 17 miles long and 1.3 miles wide.
Pirtle says Monday's twister is the first EF-5 tornado of 2013.
The state medical examiner's office has revised the death toll from a tornado in an Oklahoma City suburb to 24 people, including seven children.
Spokeswoman Amy Elliot said Tuesday morning that she believes some victims were counted twice in the early chaos of the storm. Authorities said initially that as many as 51 people were dead, including 20 children.
Teams are continuing to search the rubble in Moore, 10 miles south of Oklahoma City, after the Monday afternoon tornado.
Rescue crews worked through the night after a monstrous tornado barreled through, demolishing an elementary school and reducing homes to piles of splintered wood.
The center of the devastation is in Moore, a community of 41,000 people.
More than 120 people were being treated at hospitals, including about 50 children.
A Red Cross volunteer from central Ohio has already left to head to Oklahoma.
David Potter will spend the next two to three weeks working long hours and surviving on bare necessities.
Potter said the reward is helping victims reach for tomorrow.
"We go in and provide the most basic needs, but we help them get back on their feet, and we point them down the road to recovery," said Potter.
Potter has served in 27 disaster relief operations in the past six years, including Hurricane Sandy and the Colorado wildfires.
President Barack Obama said on Tuesday that he is instructing his disaster response team to get tornado victims in Oklahoma everything they need "right away."
Obama calls the devastation that tore through the Oklahoma City suburbs, quote, "one of the most destructive tornados in history," even though he said the extent of the damage is still unknown.
Obama spoke 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.
Obama has declared a major disaster in Oklahoma, ordering federal aid to supplement state and local recovery efforts.
The president offered prayers and said there's a long road of recovery ahead. But he said the victims won't travel alone and will have the resources they need.
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