- It was a chaotic scene in Boston as two explosives simultaneously detonated near the finish line of the marathon.
Counter-terrorism officials tell nbc news that multiple explosive devices were found at the scene. they were timed to detonate at the height of the marathon as large crowds gathered near the finish line.
"These occurred 50 to 100 yards apart," Boston Police Commissioner said. "Each one resulted in multiple casualties."
Cameras were rolling as the explosions erupted near the main grandstand where spectators had gathered.
The remaining runners were diverted and the race canceled as emergency crews rushed in.
President Obama addressed the nation.
"We will find out who did this, we will find out why they did this," the President said. "Any responsible individuals, any responsible groups will feel the full weight of justice."
Injuries are severe. Some of the victims have reportedly lost limbs.
"Everybody started running the other way, there were people running toward them to help out the injured," one witness said. "And there were some really bad bad injuries. some people were very very hurt."
The explosion was so powerful that some runners on the course were knocked to the ground while the majority of those injured are believed to be spectators.
The governor of Massachusetts is now asking boston residents to stay home.
"We are asking that people stay out of crowds and calmly make their way home," Governor Deval Patrick said.
Police and emergency officials in Boston are now dealing with a mass casualty situation as a shaken city tries to come to crips with a violent attack in the heart of the city.
Written By: NBC News