Two explosions rocked the finish line area of the Boston Marathon, causing injuries, according to media reports on Monday.
Hotels in downtown Boston were immediately locked down and police were seen in video feeds from the scene sweeping the area looking for explosions. Restaurants and bars at the finish line were shut. The area is now considered a crime scene.
An unknown number of injured have been taken to Massachusetts General Hospital, and all hotels in the area have been shut down.
There was no immediate explanation of the cause of the explosions.
Bloody spectators were seen being carried to the medical tent that had been set up for runners finishing the 26.2 mile run, the annual event in Boston.
The explosion took place about three hours after the winners crossed the line.
According to video, runners were heading to the end of the grueling race when a small explosion went off on the north side of Boylston Street, just before the bridge that marks the finish line. Automatic cameras on the bridge capture the runners as they finish.
Ethiopia's Lelisa Desisa took the title in the 117th edition of the world's oldest marathon on Monday, winning a three-way sprint down Boylston Street to finish in 2 hours, 10 minutes, 22 seconds and snap a string of three consecutive Kenyan victories.