Editor's note: Links to live coverage from Oklahoma are included at the bottom of this page.
Update posted at 11:19 p.m.:
OKLAHOMA CITY (AP) - Medical examiner: At least 20 children among the 51 killed by Oklahoma tornado.
Posted 8:34 p.m., updating an earlier version:
MOORE, Okla. (AP) - A monstrous tornado at least a half-mile wide roared through the Oklahoma City suburbs Monday, flattening entire neighborhoods and destroying an elementary school with a direct blow as children and teachers huddled against winds up to 200 mph. At least 51 people were killed, and officials said the death toll was expected to rise.
The storm laid waste to scores of buildings in Moore, a community of 41,000 people south of the city. Block after block lay in ruins. Homes were crushed into piles of broken wood. Cars and trucks were left crumpled on the roadside.
The National Weather Service issued an initial finding that the tornado was an EF-4 on the enhanced Fujita scale, the second most-powerful type of twister.
More than 120 people were being treated at hospitals, including about 70 children.
Rescuers launched a desperate rescue effort at the school, pulling children from heaps of debris and carrying them to a triage center.
Oklahoma Gov. Mary Fallin deployed 80 National Guard members to assist with search-and-rescue operations and activated extra highway patrol officers.
Fallin also spoke with President Barack Obama, who offered the nation's help and gave Fallin a direct line to his office.
Many land lines to stricken areas were down and cellphone traffic was congested. The storm was so massive that it will take time to establish communications between rescuers and state officials, the governor said.
In video of the storm, the dark funnel cloud could be seen marching slowly across the green landscape. As it churned through the community, the twister scattered shards of wood, pieces of insulation, awnings, shingles and glass all over the streets.
Volunteers and first responders raced to search the debris for survivors.
At Plaza Towers Elementary School, the storm tore off the roof, knocked down walls and turned the playground into a mass of twisted plastic and metal.
Children from the school were among the dead, but several students were pulled alive from the rubble. Rescue workers passed the survivors down a human chain to the triage center in the parking lot.
James Rushing, who lives across the street from the school, heard reports of the approaching tornado and ran to the school, where his 5-year-old foster son, Aiden, attends classes. Rushing believed he would be safer there.
"About two minutes after I got there, the school started coming apart," he said.
The students were placed in the restroom.
Douglas Sherman drove two blocks from his home to help rescue survivors.
"Just having those kids trapped in that school, that really turns the table on a lot of things," he said.
Tiffany Thronesberry said she got an alarming call from her mother, Barbara Jarrell, after the tornado.
"I got a phone call from her screaming, 'Help! Help! I can't breathe. My house is on top of me!'" Thronesberry said.
Thronesberry hurried to her mother's house, where first responders had already pulled her out. Her mother was hospitalized for treatment for cuts and bruises.
Search and rescue efforts were to continue throughout the night.
Oklahoma City Police Capt. Dexter Nelson said downed power lines and open gas lines posed a risk in the aftermath of the system.
Monday's powerful tornado loosely followed the path of a killer twister that slammed the region in May 1999.
The weather service estimated that the storm that Monday's tornado was at least a half-mile wide. The 1999 storm had winds clocked at 300 mph.
Kelsey Angle, a weather service meteorologist in Kansas City, Mo., said it's unusual for two such powerful tornadoes to track roughly the same path.
It was the fourth tornado to hit Moore since 1998. A twister also struck in 2003.
Monday's devastation in Oklahoma came almost exactly two years after an enormous twister ripped through the city of Joplin, Mo., killing 158 people and injuring hundreds more.
That May 22, 2011, tornado was the deadliest in the United States since modern tornado record keeping began in 1950, according to the National Oceanic and Atmospheric Administration. Before Joplin, the deadliest modern tornado was June 1953 in Flint, Mich., when 116 people died.
Update posted at 7:09 p.m.:
OKLAHOMA CITY (AP) - Officials at two hospitals say they're treating nearly 60 patients, including more than a dozen children, after a massive tornado hit suburban Oklahoma City.
Integris Southwest Medical Center spokeswoman Brooke Cayot (KAY'-ot) said 10 of 37 patients being treated at that facility Monday are listed in critical condition. Twelve are in serious and 15 others are listed in fair or good condition.
Five of the patients are children, including two who came from the Plaza Towers Elementary School, where an Associated Press photographer saw several children being pulled from the rubble. Cayot could not confirm the children's conditions.
Spokesman Scott Coppenbarger says another 20 patients of various ages are being treated at OU Medical Center. He says eight of them are children.
Update posted at 6:14 p.m.:
MOORE, Okla. (AP) - Several children have been pulled out of the rubble alive at a school in an Oklahoma City suburb.
An Associated Press photographer saw several children being pulled out of what was left of the Plaza Towers Elementary School in Moore, Okla., on Monday after a massive tornado hit the region.
Rescue workers lifted children from the rubble before they were passed down a human chain and taken to a triage center set up in the school's parking lot.
The school is southwest of Oklahoma City. Its roof appears mangled and the walls had fallen in or had collapsed.
The National Weather Service said the tornado's preliminary classification was an EF-4, with winds up to 200 mph.
Update posted at 5:23 p.m.:
MOORE, Okla. (AP) - A monstrous tornado as much as a mile wide roared through the Oklahoma City suburbs Monday, flattening entire neighborhoods, setting buildings on fire and landing a direct blow on an elementary school.
There were no immediate reports of injuries or deaths, but the storm laid waste to scores of buildings in Moore, south of the city. Block after block of the community lay in ruins, with heaps of debris piled up where homes used to be. Cars and trucks were left crumpled on the roadside.
Volunteers and first responders were searching through debris looking for survivors. Television footage showed first-responders picking through rubble and twisted metal.
Oklahoma City Police Capt. Dexter Nelson said downed power lines and open gas lines posed a risk in the aftermath of the system.
The storm seemed to blow neighborhoods apart instantly, scattering shards of wood and pieces of insulation across the scarred landscape.
Update posted at 4:33 p.m.:
MOORE, Okla. (AP) - Authorities say an elementary school in an Oklahoma City suburb took a direct hit from a mile-wide tornado.
Gary Knight with the Oklahoma City Police Department says there is no word of injuries from the elementary school. Knight says the school suffered "extensive damage" on Monday afternoon.
Neighborhoods in Moore, Okla., are flattened and buildings are on fire. Television footage on Monday afternoon showed homes and buildings that had been reduced to rubble in the city south of Oklahoma City. Footage also showed vehicles littering roadways south and southwest of Oklahoma City.
There were no immediate reports of injuries.
The suburb of Moore was hit hard by a tornado in 1999. The storm had the highest winds ever recorded near the earth's surface.
Update, posted at 4:14 p.m.:
MOORE, Okla. (AP) - Television footage shows flattened buildings and fires after a mile-wide tornado moved through the Oklahoma City area.
Video showed homes and buildings in Moore, Okla., were reduced to rubble, and vehicles littered roadways south and southwest of Oklahoma City.
There were no immediate reports of injuries.
The suburb of Moore, where Monday's damage was concentrated, was hit hard by a tornado in 1999 that included the highest winds ever recorded near the earth's surface.
Earlier coverage, posted at 3:49 p.m.:
OKLAHOMA CITY (AP) - A mile-wide tornado churned through the Oklahoma City suburbs, destroying homes for the second day in a row Monday, as part of a severe weather outbreak that was expected to spread in other parts of the Plains and Midwest.
A massive black-and-blue cloud dragged across the landscape just south of Will Rogers World Airport.
Television video showed debris from homes and businesses being carried aloft as the twister rolled through Moore, a community on the south side of Oklahoma City. There were no immediate reports of injuries.
In advance of the storm, the Oklahoma House of Representatives stopped work so Capitol employees could take shelter in the basement. Television and radio broadcasters urged residents to take shelter because the storm's strength and size.
"We're just waiting to see what happens. It's a mile-wide tornado. It's still grinding out," said Mark Meyers, a spokesman for the Oklahoma County Sheriff's Office. "We are currently on standby for tornado response. Whatever happens, we'll be ready to respond."
The strongest winds on earth - 302 mph - were recorded near Moore during a tornado May 3, 1999.
The Storm Prediction Center in Norman had predicted a major outbreak of severe weather Monday in Arkansas, Kansas, Missouri and Oklahoma.
Storms on Sunday killed two people near Shawnee, about 35 miles southeast of Oklahoma City. Gov. Mary Fallin earlier Monday took a tour of the areas hardest hit and she expressed concern that, with power out, Oklahomans might not receive warnings about the new round of storms.
Pottawatomie County Sheriff Mike Booth said a 79-year-old man, who was later identified as Glen Irish, was found dead Sunday out in the open at Steelman Estates, a mobile home park near Shawnee. The state medical examiner's office said Monday that a 76-year-old man, Billy Hutchinson, was found dead in a vehicle.
The office said both men lived in Shawnee, but the city wasn't hit by the tornado and it wasn't immediately clear if either or both lived in the mobile home park, which is near the city.
Live Resources:
TV coverage:
http://okcfox.com/news/features/live/
Storm chasers: http://www.chasertv.com/
Real-time updates: http://newsok.com/live-tornado-warning-real-time-updates/article/3827941
Oklahoma sheriffs' departments scanner: http://www.broadcastify.com/listen/feed/283/web
National Weather Service Oklahoma weather: http://forecast.weather.gov/MapClick.php?lat=35.4675602&lon=-97.51642759999999
How to donate to Oklahoma tornado relief: http://usnews.nbcnews.com/_news/2013/05/20/18381508-how-to-help-oklahoma-tornado-victims?lite