Multiple explosions have occurred at the finish line of the Boston Marathon on Boylston Street. There were reports of a huge boom, and then subsequent plumes of smoke rising from the side of the street. A second explosion then reportedly occurred in the same area. The origins of the explosions are still unclear, and it has not been reported what caused the blasts.
Here is video of the scene in downtown Boston from CNN's breaking news coverage:
The area where the explosions occurred is Copley Square, a busy area of the Back Bay section of Boston. It's the traditional finishing spot for the Marathon, and aside from the runners, it's filled with spectators who line the streets for the annual Patriots' Day race.
There are still no firm reports of the number of injured or potential fatalities. First responders and EMS are sweeping the area, which has been evacuated. The marathon, which has finishers crossing the line for much of the day, has been stopped.