Tornado warnings covered the map from the Ohio border to southern parts of Alabama. Greg Forbes of The Weather Channel reports.
A tornado blew a school bus into a house in Marysville, Ind.
Updated at 10 p.m. ET: Tornadoes swept across the Midwest and the South on Friday, hitting hardest in Indiana, Kentucky and Ohio, where at least 28 people were killed. An entire town was flattened in Indiana, and homes and businesses were destroyed from Ohio to the Gulf Coast.
Fourteen people were killed in Indiana, 12 died in Kentucky and two people were killed in Ohio, said The Weather Channel on its website, weather.com. It wasn't immediately clear how many people were missing.
The town of Marysville, Ind., population about 1,900, was "completely gone," and Henryville Junior-Senior High School was destroyed, Clark County sheriff's Maj. Chuck Adams told NBC News. All the students escaped, some with minor scrapes, Adams said.
"This is no place to be. We've got a terrible tragedy here, and we've got to try and deal with it," Indiana State Police Sgt. Jerry Goodin told NBC station WAVE of Louisville.
In a statement, Indiana Gov. Mitch Daniels said that despite improvements to disaster preparedness and warning systems "we are no match for Mother Nature at her worst." He said the full extent of the damage will not be known until Saturday.
Multiple tornadoes were still being reported in Georgia, North Carolina, Tennessee and Virginia well into the evening, The Weather Channel and the National Weather Service reported. At 9 p.m. ET, tornadoes were reported near the major cities of Atlanta and Knoxville, Tenn.
In West Liberty, Ky., the Morgan County Courthouse sustained significant damage, and an unknown number of people were injured or trapped in buildings. In Trimble County, Ky., a tornado leveled the Milton fire station.
The National Oceanographic and Atmospheric Administration said Friday would likely end up as one of the five biggest tornado days of the year, with "tornadic activity" leading to watches or warnings in at least 17 states.
The tornadoes began when a "very large super-cell" of tornadoes touched down in northern Alabama early in the day, damaging homes and a prison and injuring at least four people. In southern Tennessee, another twister ripped 20 homes off their foundations and submerged boats, officials said.
At least 30 people were injured in Hamilton County, Tenn., authorities told NBC News, six to 10 of them critically. "Significant damage" was reported to subdivisions along Highway 68 east of Chattanooga.
Amy Maxwell, a spokeswoman for Hamilton County Emergency Services, said at least 20 homes were destroyed and that several people were trapped beneath downed trees and structures.
To the east in Cleveland, Tenn., Blaine Lawson and his wife Billie were watching the weather when the power went out, they told The Associated Press. Just as they began to seek shelter, strong winds ripped the roof off their home. Neither was hurt.
"It just hit all at once," said Blaine Lawson, 76. "Didn't have no warning really. The roof, insulation and everything started coming down on us. It just happened so fast that I didn't know what to do. I was going to head to the closet but there was just no way. It just got us."
The Weather Channel
A Weather Channel radar map shows the breadth of the storm system at 7:15 p.m. ET, stretching from Canada to the Gulf of Mexico.
Two of the three runways at Cincinnati/Northern Kentucky International Airport were closed, and residents of Kentucky and Ohio were advised to "maintain close awareness."
At least 44 people injured in Laurel County, Ky, were taken to St. Joseph's hospital for treatment, NBC station WLEX-TV reported on its website. Officials reported head injuries, fractures as well as severe cuts. Amputations were also performed, the TV station reported.
"This is a very dangerous situation," said Tom Bradshaw, the National Weather Service's Southeast regional director.
Rare extreme warning
For only the second time, the Weather Channel issued a TORCON warning of 10 as multiple tornado-producing super-cells moved across northern Kentucky — meaning forecasters believed there was a 100 percent chance of a tornado within 50 miles. The TORCON system was developed a few years ago, and the top warning was first used April 27, 2011, during a devastating outbreak of tornadoes across the South.
Paige Colburn, an emergency management officer at the Huntsville-Madison County Emergency Management Agency, told msnbc.com that the damage in Alabama covered a 4- to 5-mile swath in northern Madison County.
"The reason that it is so wide is because we’re not talking about one tornado. We’re talking about a very large super-cell that spawned several smaller tornadoes, and there’s possibly one very large one in there, too," she said.
Maj. Chuck Adams of the Clark County, Ind., Sheriff's Office talks about the damage reported in his area. Kevin Harned of NBC station WAVE-TV reports.
Buckhorn High School sustained roof and window damage, but no injuries were reported, the state agency said in a statement. Part of the roof of Buckhorn Middle School was blown away, but all children were safe, Geraldine Tibbs, a spokeswoman for the Madison County Board of Education, told NBC News.
Back-to-back tornadoes also struck neighboring Limestone County on Friday morning. A training building at Limestone Correctional Facility, which houses 2,100 inmates, was destroyed, and two dorms and two other buildings suffered roof damage, Brian Corbett, a spokesman for the state Department of Corrections, told NBC News.
No one was hurt, and the prison was operating on generator power. The state has sent extra security, Corbett added.
March opens tornado season with a bang
A storm system earlier this week killed 13 people in four states in the Midwest and the South.
March is the start of the core of severe weather season over much of the country, said Russell Schneider, head of NOAA's Storm Prediction Center, and the "high risk" alert issued Friday — the weather service's top threat level — was the fifth during the month of March since 2000
"As far as any trends for the season, certainly this has been a very active week or two, but we really can't make any judgment on the full extent of the season at this time."
Ioanna Dafermou, Justin Kirschner, Jessica Prater, Sarah Rosefeldt, Tracy Snyder and Edgar Zuniga of NBC News; and NBC stations WAVE of Louisville, Ky., WLEX of Lexington, Ky., and WTHR of Indianapolis contributed to this report.
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