At least two people were killed and nearly 100 hurt during two explosions near the finish line of the Boston Marathon on Monday afternoon.
One blast was followed 15 seconds later by another explosion two blocks away.
For an instant, witnesses told reporters there was an eerie quiet among the carnage, not hysteria. After the second blast, people started running in all directions.
One man told the Boston Herald a leg flew near his head.
Getting outside help to the scene was difficult, authorities say, because streets were closed.
Boston Police Commissioner Ed Davis told people to stay home or in their hotel rooms.