Boston police say there's been a third explosion in the city, following two blasts near the finish line of the Boston Marathon that killed two people and injured many others.
Police Commissioner Edward Davis says authorities aren't certain that the explosion at the JFK Library was related to the other blasts, but they're treating them as if they are.
David says there are no injuries stemming from the third explosion.
He urged people to stay indoors and not congregate in large groups.
In a press conference this afternoon, officials gave out two phone numbers: Family members looking for runners can call 617-635-4500; anyone who may have witnessed anything that would help with the investigation should call 800-494-TIPS.
Gov. Deval Patrick said President Barack Obama has assured him full cooperation from the FBI and the Bureau of Alcohol, Tobacco, Firearms and Explosives as the investigation continues.
Officials are asking people to stay out of crowds and make their way home.
Reporter Jill Harmacinski heard two explosions. There are reports of deaths and people who have had their limbs blown off. The explosion was just before the photo bridge near the finish line and Lenox Hotel and was apparently outside of a building. The explosions were felt blocks away.
Bloody spectators were being carried to the medical tent that had been set up to care for fatigued runners. Police wove through competitors as they ran back toward the course.
"There are a lot of people down," said one man, whose bib No. 17528 identified him as Frank Deruyter of North Carolina. He was not injured, but marathon workers were carrying one woman, who did not appear to be a runner, to the medical area as blood gushed from her leg. A Boston police officer was wheeled from the course with a leg injury that was bleeding.
Runner Laura McLean of Toronto said she heard two explosions outside the medical tent.
"There are people who are really, really bloody," McLean said. "They were pulling them into the medical tent."
Cherie Falgoust was waiting for her husband, who was running the race.
"I was expecting my husband any minute," she said. "I don't know what this building is ... it just blew. Just a big bomb, a loud boom, and then glass everywhere. Something hit my head. I don't know what it was. I just ducked."
The Federal Aviation Administration is warning pilots that it has created a no-fly zone over the site of two explosions at the annual Boston marathon.
The agency said in a notice issued about an hour after the explosions that a no-fly zone with a 3.5-mile radius has been created over 811 Boylston St. The zone is limited to flights under 3,000 feet in altitude, which is lower than most airliners would fly except when taking off or landing.
The notice says the no-fly zone is effective immediately, and will remain in effect until further notice. Pilots planning flights were urged to call their local flight service station.