Two explosions described by race organizers as bombs went off near the finish line of the Boston Marathon on Monday as runners completed the course and thousands cheered them on. At least two people were killed and 23 injured, police said.

Video from the finish line showed screams and an enormous cloud of white smoke, and about 20 seconds between the blasts. The Associated Press reported that bloody spectators were being carried to a medical tent that had been set up to care for tired runners.