The first bomb went off at the finish line of the city’s annual cross-country marathon, exploding in a hotel lobby and ripping through the crowd. Another blast followed ten seconds later six hundred feet up Boylston Street in the major northeastern US city of Boston.

According to police officials, the bombs had been placed in trash cans, less than 100 yards apart and that they found at least two suspicious packages at other downtown locations, including a footbridge near the city’s Copley Plaza Hotel.

A third incident involving an explosion and fire was reported at a nearby library but no one was hurt, police say. Reportedly, other devices were found along the marathon route and disarmed by police.

Several are confirmed dead and death toll may rise as scores–some of whom critically- are injured.

City authorities and medical personnel reported that the casualties included children, with one of those killed identified as an 8-year-old boy. At least 10 other children were also reported among the injured, and some of the injured people had limbs amputated.

Federal authorities were treating the blasts as a terrorist attack as FBI special agent Richard Des Lauriers in Boston said an investigation is being launched by a joint terrorism task force of federal, state and local authorities. “It is a criminal investigation that is a potential terrorist investigation,” he added during a Monday night news conference.

Security was further reported tightened not only in Boston but in New York City (four hours away from Boston) and at several key locations in the capital Washington, including the US Congress and in front of the White House.

According to New York Mayor Michael Bloomberg the NYPD is on heightened alert with video of crowded areas being examined as a precaution. New York bridges, tunnels, and landmarks are also seeing more police.

There are also reports that a “Saudi national” who was injured during the incident and taken to a local hospital was being questioned by authorities. Boston Police Commissioner Ed Davis denied it Monday night, however, saying that there were no suspects but that “the police were talking to some people.”

The Boston Marathon is the oldest and most prestigious marathon in the US and it is run every year on Patriot's Day, a state holiday in Massachusetts which has been celebrated on the third Monday of April since 1897.