Shortly after tweeting photos of an engaged couple that finished the Boston Marathon, New England Cable Network reporter Jackie Bruno started tweeting about the explosion. The stark contrast between runners celebrating their finish, and the explosions that followed, is great.
A Vine video of the explosions is being widely circulated.
Social media has been a big part of the coverage.
The incident is a reminder to handle tweets carefully during breaking news situations.
Google has created a "Person Finder" to help people locate loved ones and friends.
Some have called journalists' attempts to contact sources via social media insensitive.
Some journalists are talking about CNN's decision to call the explosions a terrorist attack.
Others have commented on The New York Post's decision to report on a "Saudi suspect."