UPDATE III: Here's Steve Silva's video from Boston.com and his eye witness report:
"I was there at the finish, shooting finish line scenes, and then bang, it just went off, and then less than 15 to 20 seconds after there was a second explosion, closer to Fairfield street," Silva said."It was just immediately [evident] there were injuries, right in the middle of the spectator crowds. There was blood everywhere, there were victims being carried out on stretchers. I saw someone lose their leg, people are crying, people are confused.""It was just an explosion, it came out of nowhere. There are multiple injuries. I saw dismemberment, I saw blood everywhere. People are badly injured."
It's too early to speculate the cause or the motive, but injuries have been reported
Reuters is reporting that the headquarters at the Boston Marathon have been locked down after two explosions were reported near the finish line Monday afternoon, near the Boston Library. "There were two booms heard from near the finish line inside the Fairmount Copley Plaza Hotel," reports the AP. .
There are pictures at the link that are quite gruesome and a reporter has tweeted seeing limbs blown off.
Livestreaming here, courtesy of CNN
UPDATE: Several media outlets have reported there are three deaths at this point.
My aunt is nurse now on disaster alert at Mass General. Says several DOA's, one victim missing legs, sirens everywhere. #bostonmarathon
— Max Blumenthal (@MaxBlumenthal) April 15, 2013
Live stream from Boston's NPR station here.
UPDATE II: An 8 year old boy has been killed and the injured total has risen to 125.