ROUGH CUT (NO REPORTER NARRATION)

Video shot by a local Boston journalist on Monday (April 15) shows a fiery explosion and then a plume of heavy smoke near the flag-lined sidewalk as marathoners run by. The video shows bystanders and participants screaming and running for cover as police officers try to control the chaos.

Two explosions hit the Boston Marathon as runners crossed the finish line on Monday, killing at least two people and injuring 23 on a day when tens of thousands of people pack the streets to watch one of the world's best known marathons.

Pictures from the scene showed blood stains on the ground and several people knocked down. Massachusetts General Hospital was treating victims of the explosion in its emergency room but information about their condition was not immediately available, a spokeswoman said.

Police reported at least one explosion and witnesses said there were two, which hit as spectators were cheering on people finishing the Boston