Two explosions hit the Boston Marathon as runners crossed the finish line on Monday, killing at least two people and injuring 110 on a day when tens of thousands of people pack the streets to watch one of the world's best known marathons.
Pictures from the scene showed blood stains on the ground and several people knocked down. Massachusetts General Hospital was treating victims of the explosion in its emergency room but information about their condition was not immediately available, a spokeswoman said.
Police reported at least one explosion and witnesses said there were two, which hit as spectators were cheering on people finishing the Boston Marathon, which was first run in 1897.
Reporters in the media center heard two blasts.
Boston police had said earlier two people were killed and 23 injured.
2 more explosives discovered
A senior U.S. intelligence official says two more explosive devices have been found near the scene of the Boston marathon where two bombs detonated earlier.
The official said the new devices were being dismantled.
It was not immediately clear what kind of devices had been found Monday. The official said the first two did appear to be bombs.
The official spoke on condition of anonymity because he was not authorized to discuss the findings publicly.
A third explosion
A short while after the first set of explosions, Boston police announced a third explosion occurred at the John F. Kennedy Presidential Library and Museum in Boston after other blasts in the city near the finish line of the Boston Marathon.
Police spokeswoman Neva Coakley said "there has been another explosion at JFK."
Rachel Day, a spokeswoman for the John F. Kennedy Library, located about three miles from the marathon's finish line, said that there was a fire at the library but no one was injured.
Cellphone service were shut down in the Boston area to prevent any potential remote detonations of explosives.
Scenes of mayhem
Scores of people, some bloody, wandered the streets around the finish line, though their numbers were thinning as police, some carrying heavy weaponry, tried to clear the area and a pungent smell hung in the air.
Mike Mitchell of Vancouver, Canada, a runner who had finished the race, said he was looking back at the finish line and saw a "massive explosion."
Smoke rose 50 feet (15 metres) in the air, Mitchell said. People began running and screaming after hearing the noise, Mitchell said.
"Everybody freaked out," Mitchell said.
Ambulances, fire trucks and dozens of police vehicles converged at the finish line.
U.S. President Barack Obama was notified and directed his administration to provide whatever assistance was necessary, the White House said.
"Blood everywhere, victims carried out on stretchers. I saw someone lose their leg, people are crying," the Boston Globe's Steve Silva reported from the citing, the Globe said on Twitter.
Hundreds of thousands of spectators typically line the 26.2 mile (42.19 km) race course, with the heaviest crowds near the finish line. The blasts occurred more than five hours after the start of the race, at a time when most top athletes were off the course but slower amateur marathoners were still running.
The transit agency shut down all service to the area, citing police activity.
Ambulances arrived on the scene within minutes and runners and spectators could be seen crying and consoling each other.
The Boston Marathon has been held on Patriots Day, the third Monday of April, since 1897. The event, which starts in Hopkinton, Massachusetts and ends Boston's Copley Square, attracts an estimated half-million spectators and some 20,000 participants every year.
Earlier on Monday, Ethiopia's Lelisa Desisa and Kenya's Rita Jeptoo won the men's and women's events, continuing African runners' dominance in the sport.
The New York Police Department stepped up security around landmarks in Manhattan, including near prominent hotels, in response reports out of Boston, said Paul Browne, deputy commissioner of the NYPD.
New York police were redeploying counterterrorism vehicles around the city, Browne said.
No threats detected before explosions
Boston Police Commissioner Ed Davis said on Monday that officials did not know of any specific threats before three devices exploded in Boston on Monday that killed at least two people.
He said that local police is getting aid from every agency in the state and the federal government after the explosions which occurred close to the finish of the Boston Marathon.
"Every asset of the Commonwealth of Massachusetts and the federal government is either here or is coming here," Davis said. One other explosion occurred at the John F. Kennedy Presidential Library.
Speaking at a news conference at a hotel near the finish line of the Boston Marathon where two of the three explosions went off, Davis said that anything left on the streets is currently being treated as a suspicious device.