Broadcast and cable news outlets were forced into the all-too-familiar ritual of covering a jarring national tragedy on Monday after two bomb explosions rocked the Boston Marathon, killing at least three people and injuring more than 100.

The major news outlets broke into regular programming shortly after the explosions, which hit at about 2:45 p.m. ET, four hours after the start of the race. The networks summoned top anchors and other resources to go wall-to-wall with coverage of the chaotic scene, some of which included graphic pictures of marathon runners and bystanders with serious injuries. By early evening, NBC had tabled its skedded 10 p.m. airing of drama “Revolution” for a news special on the bomb blasts.

Within minutes of the explosions, Twitter was flooded with graphic images and Vine videos from the scene, with ABC News’ Diane Sawyer noting that the Boston Police Department sought “every possible photo” from the public in order to aid the investigation. News nets were forced to contend with speculation that ran rampant on Twitter regarding the nature of a fire at the JFK Library, and the death toll, which the New York Post labeled as “10” before law enforcement had even confirmed two.

The jolt of the attack was magnified by the fact that marathon day is a major celebratory event in Boston (it falls on Patriots’ Day, which is a holiday in Massachusetts), as President Obama noted in a somber statement that decried the “senseless loss” and vowed that authorities “will get to the bottom of this.”

The marathon draws about 23,000 runners and typically about 500,000 spectators. The first explosion went off in a trash can near the finish line. The second went off a few seconds later several hundred yards away, according to the New York Times. There were reports that authorities found several other devices, at least one of which was detonated by police in a controlled blast.

Boston Globe reporter David Abel, who was 10 feet away from one of the bomb sites, tweeted:

Given the media presence at the marathon, news nets captured footage of the explosions themselves and rebroadcast them in their breaking news coverage. In some clips, runners are seen collapsing in the wake of the explosion. In others, blood-stained sidewalks are visible, as are graphic scenes of medical teams tending to dazed victims. CBS News had access to footage captured by its Boston O&O WBZ-TV, which had local TV rights to the marathon.

NBCUniversal’s Universal Sports Network, which had national cable rights to the marathon, issued a statement via CEO David Sternberg: “We have suspended coverage and have cancelled all re-airs of today’s race. Our thoughts and prayers are with those who are injured.”

As law enforcement officials erred on the side of caution when it came to safety measures after the blasts, news nets employed a similar level of caution when it came to linking the explosions to a terrorism, dubbing the explosions “blasts” and not “bombs” during a good part of their early coverage. A conservative approach was also taken by nets as they avoided the use of the phrase “terrorist attack” until the government and law enforcement officials brought those words into the language of the day’s events.

The New York Times cited reports from law enforcement sources that a 20-year-old Saudi man was among several people being questioned in connection with the blasts, though no arrests had been made as of Monday night.

Whitney Friedlander also contributed to this report.