At least two people are dead and 22 have been injured, according to the Boston Globe (23, according to NBC Nightly News, citing Boston police), in what appears to be an attack at the Boston Marathon. Boston.com, which is liveblogging the race, reports that two explosions were heard close to the marathon's finish line.
Media are currently being held in lockdown at the Fairmont Copley Hotel, and ambulances are arriving. Bystanders reported a large explosion and more information will be posted as it becomes available. One marathon participant, Foursquare's Dennis Crowley, tweeted that a large number of racers are in corral close to the finish line.
Unconfirmed reports from Twitter users are reporting "unspeakable horror."
One of the explosions was captured on local television and turned into a Vine.
A Boston police spokesperson told Reuters that "There was an explosion. Police, fire and EMS (emergency medical services) are on the scene, we have no indication of how many people are injured."
Jim O'Sullivan of the Boston Globe reported on Twitter that police have found "secondary devices" at the scene. And AP reports that a senior U.S. intelligence official says two more explosive devices have been found and are being dismantled.
The Boston Police Department has confirmed explosive devices were found along the parade route. A third explosion also went off but police were "aware of it ahead of time"; it is not known whether that explosion was a controlled demolition.
Before the race, there was a dedication marker installed memorializing the victims of the Sandy Hook Elementary shooting in Newtown at mile 26—to mark both the last stretch of the race and the number of lives lost. "When we hit Boylston Street, and we run that final 385 yards towards the finish, we're going to sprint that we ran that day like we ran to get to our children," Dr. Laura Nowacki told Boston CBS affiliate WBZ earlier this month. Her daughter survived the Sandy Hook massacre—Nowacki is also a pediatrician to eight Newtown children who died. She planned to run the marathon on Monday. "We're going to fly like those little kids flew to get out of that horror," she said.
In the wake of the tragedy, Google has launched a Boston Marathon Explosions People Finder to allow loved ones to quickly find information about the loved ones. The technology used in the Boston people finder was leveraged from a previous Google project to find out information about victims of the Haiti earthquake.
At this time, law enforcement authorities believe that small improvised bombs were planted among the crowd at the Boston Marathon finish line.
As a result of the incident, mobile phone service in Boston has been temporarily disrupted. The Associated Press reports mobile phone service has been turned off in Boston due to law enforcement fears that phone lines could be used for remote detonation of explosives.
On Monday evening, President Obama spoke to the American people, vowing to catch whoever was responsible for the tragedy. "We still do not know who did this or why. But make no mistake," he said. "We will get to the bottom of this."