Panic instantly rented the atmosphere everyone started making ways to rescue the injured while rescue operations went to work immediately.
Witnesses said the streets were littered with debris and blood and described paramedics racing off with stretchers. TV footage showed an explosion sending up a white plume of smoke along the side lines of the race.
According CNN report on the blasts, at least six people were wounded.
According to witnesses, the first explosion took place near a sports store and the second went off near a viewing stand.
It was not immediately clear whether the explosions were accidental.
Zara Bielkus, a 30-year-old spectator from Boston, said she heard two explosions seconds apart. Police then locked down the area.
The Boston Marathon is one of the biggest annual athletic events held in the United States, with nearly 27,000 racers who must qualify to compete and tens of thousands of spectators.