Boston Marathon organizers say two bombs went off near the finish line of the race. As of April 16, three are dead, including an 8-year-old boy, and at least 170 people are injured.

According to MSNBC, the explosions were strong enough to cause at least one runner to collapse, and emergency personnel carried bloody spectators away.

Race organizers, in a post on Twitter, said: “There were two bombs that exploded near the finish line in today’s Boston Marathon. We are working with law enforcement to determine exactly what happened.”

Barack Obama was notified, and his administration was in touch with state and local authorities, a White House official told NBC News. Obama directed the administration to provide whatever help was necessary, the official said. In a press conference Monday, Obama stated that the responsible parties are as of yet unknown, but they will know the full weight of justice. He also declared the bombing an act of terrorism.

Suspicious packages were found after the blasts at three Boston subway stops, and authorities were investigating. Within an hour of the blasts, New York police deployed extra security to landmarks, and Pennsylvania Avenue in front of the White House was closed to foot traffic. San Francisco put its police on heightened alert.

The race is a signature event in Boston and has been run since 1897 on Patriots Day, the third Monday in April. Tens of thousands of spectators turn out each year to watch.

The race began at 10 a.m., and the explosions were reported just before 3 p.m.