Boston Marathon 2013 UPDATE: Explosion Heard at Finish Line, Some Injured

Two explosions were heard around the vicinity of the finish line at the Boston Marathon on Monday, breaking upbeat spirits and positive forecasts of good weather.

Witnesses like Will Ritter, spokesperson for a Massachusetts Senate Candidate told NBC News that he "heard what sounded like two explosions and saw smoke rising near the Boston Public Library." He also mentioned that three fire engines and police ran to the site, amidst runners and spectators who had hit the pavement.

Others fled wildly, crying and running in the swirls of smoke.

Many were injured, according to Frank Deruyter, a participant from North Carolina. He told the Associated Press , "there were a lot of people down," and that he saw marathon employees carrying one woman who did not look like she was a participating runner, to the medical tent as blood flowed from her leg.

A police officer was also seen being taken from the course with a gushing leg. Boston Marathon headquarters are now on lockdown, according to Reuters.

Federal authorities have told various news services that they do not have any immediate information.