Site of Boston explosion
Site of Boston explosionReuters

At least two people are dead and 73 injured after two bombs tore through the finish line of the Boston Marathon, according to the Boston Police Department.

Authorities were guarding a person of interest at a local hospital, reported Fox News. The person, who sources said was 20 years old, had severe burns, but authorities had not determined whether the person was a victim or a perpetrator. Boston Police Commissioner Edward Davis said during a press conference that no suspect is in custody. 

Police did not immediately say whether the explosions were part of a terrorist attack, but marathon organizers said it was a twin bombing and media outlets reported that other unexploded devices had been found nearby.

CNN reported that a third explosion happened at the John F. Kennedy Presidential Library, which is located about five miles southeast of the Boston Marathon finish line.

The library later said there was an electrical fire that had been extinguished without causing any injuries.

Massachusetts General Hospital told CNN it was treating 19 injured people; Tufts Medical Center reported that some injured were to be treated there as well.

The explosions sent smoke billowing into the air at Copley Square, turning a site of celebration into a mess of destruction, according to CNN.

According to CBS News, two bombs were inside trash cans near the viewing area close to the finish line. One unexploded device has been recovered, according to CBS.

Officials in other cities, including New York, tightened security as a result of the Boston blasts.

Mike Baingon, who works at the Atlantic Fish Company in Boston, said an explosion took place in front of the restaurant and that he was right by the front door at the time.

The explosions occurred at about 2:45 p.m., more than two hours after the first of the race's nearly 27,000 runners had crossed the finish line.

Security was stepped up in New York and Washington, sites of the 9/11 attacks, reported AFP. In the Big Apple, police said they were boosting security at hotels and "other prominent locations in the city."