The cable news networks pivoted to breaking news in Massachusetts shortly after 3pmET Monday afternoon as two explosions went off at the finish line of the Boston Marathon.

Fox News was the first cable news network to report the news at 3:06:18 p.m., followed just seconds later by CNN at 3:06:53 p.m. MSNBC reported the news at 3:08:45 p.m. All three cable news networks were several minutes minutes behind the first reports of the explosions on Twitter.

Fox News and CNN are relying on live pictures from Boston local stations. MSNBC has video from New England Cable News, which is owned and operated by NBC Universal.

> More: The broadcast networks also broke in with news of the explosions. CBS News was first at 3:10pmET, followed by ABC News and NBC News at 3:13 p.m. Scott Pelley is anchoring on CBS, Brian Williams on NBC and Diane Sawyer and George Stephanopoulos on ABC.

> More: Matt Frucci, the incoming executive producer of CNN’s new morning show, is doing eyewitness reports from the scene for the network. Wolf Blitzer is anchoring. And on Fox News, Shepard Smith is talking with WGBH’s Emily Rooney, former network executive and daughter of Andy Rooney.

> More: Anderson Cooper is on his way to Boston and will anchor at 8pmET and 10pmET.

> More: Here’s affiliate video of one of the explosions, as seen on CNN:

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Bloomberg TV is adding another hour of “Bloomberg West,” anchored by Emily Chang, Cory Johnson and Jon Erlichman, to its lineup next week. Along with the existing hour of the San Francisco-based tech show, which airs at 6pmET/3pmPT, a new hour will be added at 1pmET/10amPT beginning Monday.

The expansion sets off a domino effect of programming changes in the rest of the network’s lineup. “Money Moves with Deirdre Bolton” moves from 1pmET to 2pmET, while “Bottom Line with Mark Crumpton” moves from 2pmET to 7pmET. “Bloomberg Rewind,” a recap of the day’s top stories that aired at 7pmET, will be removed entirely from the lineup.

The New York Times‘ Quentin Hardy has more on the expansion:

“We see a real opportunity,” said Andrew Morse, head of Bloomberg Television in the United States.

“The television world is flooded with mediocre content — this extra hour is more of a place for big names in the Valley to come on and talk, and to dig deeper into what the news means,” he said, speaking of Silicon Valley.

The business networks are gearing up for tomorrow’s Facebook IPO, which begins trading on the NASDAQ when the markets open tomorrow morning.

Bloomberg TV is kicking off coverage at 5pmET today with “Facebook: The Public Network,” a live three-hour special anchored by Emily Chang and Cory Johnson in San Francisco, Betty Liu in New York and Jon Erlichman at Facebook’s headquarters in Menlo Park, CA. At 8pmET, Matt Miller will anchor a live one-hour special, followed by an updated version of Bloomberg’s “Game Changers” on Mark Zuckerberg at 9pmET.

CNBC devoted the 1pmET hour this afternoon to the IPO with a special anchored by Carl Quintanilla. He and Julia Boorstin will also report from Facebook’s headquarters tomorrow. Tomorrow morning, CNBC’s “Squawk on the Street” will broadcast from the NASDAQ, where Facebook will be trading, instead of their usual perch at the NYSE.

On Fox Business Network, Stuart Varney will host a special “Varney & Co.” tomorrow morning to cover the market open and the IPO launch. Shibani Joshi will be live from Facebook’s headquarters and Lauren Simonetti will be at the NASDAQ.

This week marks one year on the air for “Bloomberg West,” the daily technology and innovation show on Bloomberg TV.

Anchor Emily Chang told TVNewser the show’s home base in San Francisco provides an insider perspective on the tech industry.

“I love tracking the incredible rise of companies like Facebook and Twitter, love being part of covering what might be ‘the next big thing,’ and there’s no better place to do that than San Francisco,” Chang told TVNewser. “We’re covering today’s industrial revolution.”

Chang, along with Cory Johnson and Jon Erlichman, have led Bloomberg’s coverage of the major tech news of the past year, including the death of Apple CEO Steve Jobs, Facebook filing for its IPO and Groupon going public.

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