BOSTON -- At least three people are dead and 100 injured after two bomb blasts shook the site of the Boston Marathon finish line Monday afternoon, with a third, possibly related incident an hour and a half later, reported at Boston's John F. Kennedy Library.
Spectator video from the finish-line explosion shows marathon fans being pushed off of the Boylston Street sidewalk by the concussions, the smoke of the blasts blowing through the international flags lining the finish chute.
Medical treatment of bystanders' most severe injuries included amputations after what were thought to be low-angle explosions at near range.
The library incident has at various times been described by officials as an electrical fire and an explosion. As of Monday evening, officials could neither confirm nor deny the presence of any sort of explosive device at the library site.
Massachusetts Gov. Deval Patrick urged Bostonians and visitors to stay lodged away for the night.
"It's best that most people make their way calmly home, and if they're in the city, back to their hotels," Patrick said.
Those hotels in many cases have additional police security, according to Boston Police Commissioner Ed Davis.
Visitors at one of those hotels -- the Fairmont Copley Plaza, two blocks from the marathon finish-line site -- were able to feel the concussions, with several on the first floor commenting that it felt as if something large had been dropped.
While most reporters covering the marathon in the hotel's media room were unable to reach the area because of lockdown procedures at the hotel's press center, photos and video of the detonation were widely available on social media shortly after it occured.
"I was about to turn the last corner from Hereford Street onto Boyleston when I heard two successive blasts," wrote David Chen, a marathoner from Annapolis who told about his experiences in an email to a Sun staffer.
"I see the police all look at their radios with a look of disbelief. Rounded the corner as this is happening only to have a line of police meet all the runners and say we're stopping the race, move to the sidewalks," Chen wrote.
"Rightfully so, BPD is jittery and wants everyone to go home. 'Clear the area' is the order. Only problem is I don't know Boston well enough. All public transport is shut down."
The marathon finish line facilities were closed shortly after the blasts, and police and fire crews -- already active for the race itself -- brought brought additional forces to the scene of the explosions.
What had been a medical tent for the marathon was turned into a triage facility, with ambulances continuing to arrive until nearly an hour after the incident.
Shortly after the blasts, runners remaining on the course were diverted down Commonwealth Avenue -- more than 5,000 of the 23,326 initial starters, according to race officials -- and nearly an hour after the original explosions, most people had been evacuated from the blocks around the area.
A few remaining onlookers were alarmed at the sound of what turned out to be a water cannon. As of 5:54 p.m., marathon officials said the Boston Police Department was continuing to find "multiple devices" in the area.
Significant portions of the Boston metro area's transit infrastructure had by that time been shut down as a precaution.
"This is a tragedy," said Boston Mayor Tom Menino at 6 p.m.
"We're going to work together on this."
Getting in touch
As of Monday evening, some families were still looking for their runners, who were diverted from the finish line and dispersed.
People who had been near the site wandered through Boston's streets, moving away from what was now a working crime scene on Copley Plaza. Mobile phone service remained spotty or intentionally disabled, shut down by police to prevent any possible remote detonations. Google set up a person finder.
Many people remained locked inside hotels. Charlotte Rocker, a runner who finished roughly seven minutes before the blasts, managed to leave her hotel just before it went on lockdown.
When the explosions occured, "I was about 300 feet from the finish line," Rocker said Monday evening. "They give you food and they give you a blanket ... we were sort of making our way through all that."
"I'm 28 years old and I've never seen my father cry, but when I got there he was just hysterical."
Rocker was impressed by the responses she saw, both at the site and online.
"The outpouring of support from all corners has just been very meaningful," Rocker said.
"The stories I've heard about runners who crossed the finish lines and went straight to donate blood ... runners who finished up and then immediately went to help at the medical tents."
"This was the third wave of runners," Rocker said. "That's basically all charity runners ... those are the people who suffered from this."