Blasts near the finish line of the Boston Marathon killed two people and injured at least 22 others this afternoon; the toll is rising. Smoke billowed into the air over Copley Square, turning the annual celebration into panic and mass evacuation.

Around 2:45 PM, about two hours after the race started, the Boston explosions occurred. Authorities did not immediately say what caused the explosions. On its Facebook page, the marathon itself referred to the blasts as bombs.

Video footage showed an explosion as runners neared the finish line near Boylston and Exeter streets. The impact, which occurred about 300 yards from the line, knocked some runners over. About ten seconds after the first blast, a second occurred on the opposite side of the street.

Photos of the scene showed a sidewalk slippery with blood and blown-out store-fronts. Emergency personnel raced to the scene and cordoned off the area. A Boston firefighter tweeted that there may have been "another possible device" at the Mandarin Hotel nearby, but this has not yet been confirmed. At least one of the blasts may have come from a trash container.

Massachusetts General Hospital said it was treating 19 injured people; Tufts Medical Center reported that some injured were to be treated there as well but did not give an exact number. Many of the injured appear to be spectators.

Over 27,000 runners were participating in the marathon this year. Crowds had gathered to watch the runners along the route, and many bystanders are shaken up. The race was halted following the incident. Subway service in the area was also shut down. National Guard troops are assisting police in recovery efforts.

A White House official said President Obama was notified of the incident, and the President directed his administration to provide whatever assistance is necessary to aid local and state authorities in response and investigation of the incident.