At least two people are dead and dozens more injured after an apparent terrorist attack on the Boston Marathon.
Two explosive devices detonated near the race finish line.
"There was one right at finish line, it sounded like a huge cannon went off, and then another one happened right across from us," said one witness. "It was just a huge explosion and there was just debris everywhere."
The blasts were so powerful that some runners were knocked to the ground.
The majority of those wounded, however, were bystanders.
Security has been tightened across Boston and in other major cities.
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