4:27 p.m.: Speed and strength of the tornado upgraded to a top-of-the-scale EF-5 with winds of at least 200 mph, according to the National Weather Service.
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3:53 p.m: Survey crews find damage in one area equal to an EF5 tornado, according to the National Weather Service.
1:31 p.m.: 38,000 people are without power in areas around Oklahoma City, Gov. Mary Fallin says.
1:30 p.m.: Total number of missing people still unknown, says Oklahoma governor.
1:21 p.m: "We will overcome. We will rebuild. We will regain our strength," said Gov. Mary Fallin.
1:15 p.m.: FEMA director Craig Fugate is on the ground in Oklahoma, according to White House officials. Homeland Security Secretary Janet Napolitano will fly there Wednesday. No decision has been made on when President Obama might tour the damage.
11:58 a.m.: The National Weather Service predicts strong winds and hail for Moore, Okla., potentially complicating search and rescue efforts.
11:50 a.m: The Oklahoma Medical Examiner's Office has revised the death toll to 24 people, including nine children.
11:35 a.m.: Oklahoma Gov. Mary Fallin will hold a press conference at 1 p.m. ET.
11: 30 a.m.: Oklahoma University Medical Center says it has 85 patients, 50 of whom are children. Injuries range from minor to critical, according to hospital staff.
10:10 a . m . : President Obama announces that FEMA search and rescue teams from three states have been ordered to Moore. "The people of Moore should know their country will remain on the ground, beside them for as long as it takes," the president said.
10:08 a.m.: "In an instant, neighborhoods were destroyed. Dozens of people lost their lives. Many more were injured and among the victims were young children trying to take shelter in the safest place they knew, their school," says President Obama.
9:55 a.m.: State Medical Examiner says confusion over the number of deaths was the result of double counting victims. Some 242 people have been treated for injuries, at least 58 of them children, according to authorities.
9:24 a.m.: Oklahoma Medical Examiner reports 24 people dead, seven of which are children, dramatically lowering the number of people believed to have died in Monday's tornado. On Monday night, authorities estimated the number of deaths at 51.
7: 15 a.m.: Oklahoma Gov. Mary Fallin told " Good Morning America," "It's a very sad day in Oklahoma. A lot of hearts have been broken."
6:43 a.m.: President Obama will deliver a televised statement regarding the Oklahoma tornado at 10 a.m. ET.
6:28 a.m.: Pope Francis tweeted, "I am close to the families of all who died in the Oklahoma tornado, especially those who lost young children. Join me in praying for them."
5:33 a.m.:McClain County Animal Response Team spokeswoman Patty Mannas told ABC News affiliate KOCO-TV that at least 50 pets have been pulled from the rubble in Moore, Okla
"We've already reunited a few animals and animals with microchips have a very, very high percentage of being reunited with their families," she said.
4:20 a.m.: The death toll remains at 51, but the Oklahoma Chief Medical Examiner said it expects to find about 40 more bodies.
2:50 a.m.: Moore officials tell ABC News the search and rescue operation at Plaza Towers Elementary School is now a recovery effort.
12:50 a.m.: Texas Task Force 1, the state's elite search and rescue team, has been activated to assist local officials and first responders in Oklahoma. The team, which includes 84 total members, was deployed to New York City following 9/11 and to New Orleans in the aftermath of Hurricane Katrina. It was recently deployed to West, Texas, following the explosion of a fertilizer plant.
Monday's devastating tornado that ripped through Moore, Okla., killed at least 51 people, including 20 children, but authorities expect that number to rise. Spokeswoman Amy Elliott of the Oklahoma City Medical Examiner's office said she believes at least 91 people are dead.
All times indicated in this live blog are in Eastern Daylight Time.
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