The explosions sent smoke billowing into the air at Copley Square, turning a site of celebration into a mess of destruction.
“It felt like a huge cannon,” a witness told CNN about one of the blasts.
A third explosion occurred at the John F. Kennedy Presidential Library and Museum in Boston, a half hour after the initial blasts. Authorities said it’s unclear if the incidents are related, but are investigating them as if they were.
Authorities in Boston have found other explosive devices that they were working to dismantle, a federal law enforcement source told CNN. The devices were “low flashpoint,” and did not appear to have shrapnel inside them, the source said.
It was unclear who may have planted the bombs. There were no credible threats before the race, a state government official said.
Out of an abundance of caution, the Lenox Hotel was evacuated, the Boston Globe reported, as authorities looked into possible security concerns.
Massachusetts General Hospital said it was treating 19 injured people, six of them in critical condition. Tufts Medical Center reported that it was treating nine people. Combined, that brings the number of injured to at least 28. Police reported 22 people injured.
Crowds were in the area watching the runners when the blasts took place.
“We are currently in contact with federal, state and city officials,” Massachusetts Gov. Deval Patrick wrote on Twitter.