Two explosions took place around 3 p.m., within seconds of each other, on Monday at the Boston Marathon.

The first runners in the marathon crossed the finish line around noon. Boston Police Department said two explosions took place on Boyleston street near the finish line of the Boston Marathon. Police, fire and bomb squad responded. Massachusetts General Hospital confirmed at least four are injured.

A trauma nurse told ABC News that the race's medical tent has turned into a morgue, as they deal with injuries including severed limbs and children with severe burns.

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Police, fire and EMS (emergency medical services) are on the scene, but there is no indication of how many people are injured, a spokeswoman for the Boston Police Department said.

The Boston Marathon has been held on Patriots Day, the third Monday of April, since 1897. The event starts in Hopkinton, Mass., and ends Boston's Copley Square. At least three people are dead and dozens injured - including up to 10 with amputated limbs, according to Fox.