Television news organizations are scrambling to get teams in place to cover the horrific shooting at Sandy Hook Elementary School in Newtown, Conn., that has so far has left 20 children and six adults dead, including the shooter.

Broadcast news divisions are sending their lead anchors to Newtown, which is in Fairfield County, about an hour and 15 minutes from New York City. ABC's Diane Sawyer, CBS' Scott Pelley and NBC's Brian Williams will anchor their network's respective evening news broadcasts from Connecticut.

"CBS Evening News" will expand to one hour, and the network also will crash an hourlong special on the shooting set to air at 10 p.m. Friday.

ABC's "World News" also will present a one-hour edition of while "20/20," at 10 p.m., will cover the shooting, with Sawyer and Chris Cuomo anchoring; "Nightline" also will use its entire half-hour to address the tragedy.

NBC's "Nightly News" will fill an hour and the network's regularly scheduled 10 p.m. edition of "Dateline" will cover the shooting with Williams and Lester Holt anchoring.

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Cable news has been covering the shooting wall-to-wall since about 10 a.m. ET, while local stations in New York have blown out regularly scheduled programming to report on one of the worst school shootings in U.S. history, which nearly doubled the death toll of the 1999 shooting in Columbine, Colo.

NBC's Holt has anchored multiple special reports on the network that have featured justice correspondent Pete Williams, White House correspondent Kristen Welker, former FBI profiler Clint van Zandt and correspondent Tom Costello (who is from Littleton, Colo., near Columbine).

On CBS, Rebecca Jarvis and John Miller broke into daytime programming at 12:07 p.m. ET, with "CBS This Morning" co-anchor Norah O'Donnell taking over for Jarvis, who is traveling to Newtown.

ABC's David Muir began anchoring the network's coverage after Sawyer was dispatched to Connecticut. Dan Harris also is at the scene.

Fox News Channel also has shifted the entire day's coverage to Newtown, with at least five members of the network's roster -- correspondents Rick Leventhal, Molly Line and Jonathan Hunt, anchor Bill Hemmer and host Greta Van Susteren -- all on location at some point Friday. Leventhal was the first to arrive, with Line and Hunt in route just before 2 p.m. ET. Hemmer and Van Susteren will host their regularly scheduled broadcasts from Connecticut. The "O'Reilly Factor" and "Hannity" will air in their regular time slots, also devoting their hours to the shooting. The weekend schedule is also expected to change, with "Fox & Friends" starting earlier at 5 a.m. on Saturday, though full plans were not immediately available.

MSNBC first reported the shooting at 10:37 a.m. but currently has no plans to send one of its primetime hosts to the scene.

At about 2:20 p.m., news organizations identified the shooter as Ryan Lanza, 24, of New Jersey, and said his mother - a kindergarten teacher at the school - was one of the adult victims killed at the school. Connecticut authorities said during a press conference that the shooter died at the scene.

[Update: As of 3:40 p.m., multiple outlets were reporting Adam Lanza, 20, to be the shooting suspect, and identifying Ryan Lanza as an elder brother. Also, a brother was discovered dead at the shooting suspect's home, according to police.]

Witnesses said the shooter entered the school with two 9mm handguns, firing dozens of shots. Most networks and the AP were reporting that Lanza killed 26 people.

The reported number of people killed fluctuated as the story was unfolding during the late-morning hours; as late as a few minutes before 2 p.m., CNN still was reporting that only 20 people were killed before updating that count to "close to 30."