(CNN) — Two bombs struck near the finish line of the Boston Marathon on Monday, killing two people and injuring at least 28.
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.
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.
U.S. Attorney General Eric Holder spoke with FBI Director Robert Mueller and U.S. Attorney Carmen Ortiz, a Justice Department official said.
Holder has directed the full resources of the Justice Department to be deployed to ensure the matter is fully investigated, the official said.
The Federal Aviation Administration placed a flight restriction over the site of the blasts.
Other cities, including New York and Washington, tightened security as a result. Following standard protocol, the White House cleared out an area in front of the West Wing.
“If you see something, say something,” Mark Boughton, mayor of Canbury, Connecticut, wrote on Twitter. “All cities will be on a heightened state of alertness per Homeland Security protocols.”
Mike Baingon, who works at the Atlantic Fish Company in Boston, said an explosion took place in front of the restaurant and that he was right by the front door at the time.
The explosions occurred at about 2:45 p.m., more than two hours after the first of the race’s nearly 27,000 runners had crossed the finish line, CNN Producer Matt Frucci reported.
The race was halted as was subway service into the area.
Runners east of Massachusetts Avenue were directed to Boston Common; those west of Massachusetts Avenue were directed to Kenmore Square, the state’s emergency management agency said.
Troops from the Massachusetts National Guard were assisting police as well.