Two bombs struck near the finish line of the Boston Marathon on Monday, killing two people and injuring at least 23 others, Boston police said.
A third blast then followed at the John F. Kennedy Presidential Library, which authorities believe was related, Boston Police Commissioner Ed Davis said.
"We are not certain that these incidents are related, but we are treating them as if they are," Boston Police Commissioner Ed Davis told a news conference, according to Reuters.
The explosions occurred about 3pm ET, about 4.5 hours after the start of the race, just feet away from the finishing line along Boylston Street, where hundreds of runners were gathered as the world's oldest annual marathon. Copley Square Mall closed all its stores and no one could access the Mall at Prudential Center, which is at the finish line.
Facebook and Twitter were buzzing with photos of the pavement along the final stretch of the race covered in injured people being attended by security guards and emergency workers. There was no information from police on the cause of the blasts, but the marathon organizers said on their official Facebook page that they were the result of two bombs.
Massachusetts General Hospital was treating 19 victims of the explosion in its emergency room, six of them in critical condition, a spokeswoman said.
Security was later stepped up in New York city, with the NYPD's critical response vehicles being deployed, though it was not clear whether the move was a routine precaution or based on any specific intelligence.
Before the bomb blasts occurred, Ethiopia's Lelisa Desisa and Kenya's Rita Jeptoo won the men's and women's events, continuing African runners' dominance in the long distance running sport.
Watch a live feed on the Boston Marathon Bombing from ABC here.
