The Boston Marathon turned from a test of endurance into a scene from a war zone in moments as twin blasts, 12 seconds apart, rocked the finish line. Over 140 people were injured, with three killed, including an eight-year-old boy.

Two explosions occurred near the finish line of the 26.2-mile (42km) event at 2:50pm local time (18:50 GMT). The attack left sidewalks covered in blood and injured piled on top of one another, with many receiving serious injuries, including lost limbs. The marathon gathered half a million people from 50 nations.

The authorities have not officially confirmed whether the explosions were a terror attack or not and no suspects have yet been identified.

Federal aviation authorities have declared a no-fly zone over the area and authorities including the US Air Force continue to attempt to secure the scene. The aviation restrictions have reportedly extended to an order that all flights out of Boston’s Logan Airport be grounded until further notice.

An intelligence official working on the scene told the Associated Press that two additional explosive devices were found inside garbage cans near the site. Other reports say there were a total of five unexploded devices found following the blasts.

As law enforcement look for further explosives, they have reportedly told people in the area to stay off mobile phones for fears that the signal could detonate another undiscovered device.