As the magnitude of the Las Vegas shooting rampage sank in Monday morning, producers and anchors of the Big Three nightly newscasts scrambled to get on the ground there for extended broadcasts tonight from the site of the deadliest mass shooting in U.S. history.

CBS News confirmed that “CBS Evening News” anchor Anthony Mason would helm an hourlong telecast tonight from Las Vegas. NBC News’ Lester Holt will anchor an extended “NBC Nightly News” from the city. ABC News’ David Muir do the same for an hourlong edition of “World News Tonight.”

MSNBC said Chris Hayes and Rachel Maddow will host special editions of their primetime shows from Las Vegas tonight.

The attack by a suspected lone gunman on a country music festival in Las Vegas on Sunday night left more than 50 people dead and more than 400 injured. The suspected gunman, who fired from a window on the 32nd floor of the Mandalay Bay hotel, was found dead by what police were calling a self-inflicted gunshot wound.

As of midday, the Big Four networks had no plans to preempt primetime programming for additional news coverage. Undoubtedly, network programming executives spent Monday combing their schedules to look for storylines that might ring too close to the shocking incident in Las Vegas. Networks typically are quick to pull narrative programs that mirror real-world tragedies.

TV news outlets have been in wall-to-wall coverage mode as the nation grapples with the aftermath of the horrific violence that turned a parking lot outside the Mandalay Bay casino into a war zone. The suspected gunman, identified as 64-year-old Stephen Paddock of Mesquite, Nev., is estimated to have fired 200 rounds from a high-powered machine gun through a window on the 32nd floor of the hotel that overlooked the crowd of about 22,000 people gathered for the Route 91 Harvest festival.

(Pictured: NBC News anchor Lester Holt)