The Boston Globe is reporting that at least a dozen people have been seriously injured. CBS Boston is reporting that 20-30 have been injured. According to police scanner radio, the bomb apparently came from a suspicious package under the bleachers.
UPDATE, 3:20 p.m.: Reporters and runners are tweeting images and reactions from the finish line
UDPATE, 3:54 p.m.: The Boston Police Department has made its first statement via Twitter.
UPDATE, 3:35 p.m.: Screencaps of the explosion from CBS Boston.
UPDATE, 3:39 p.m.: Fox reports three dead; NYC counterrerorism unit on its way to Boston.
Shepard Smith of Fox News is reporting that three people are dead as a result of the explosion. They also report that New York is sending a counterterrorism team to assist Boston police.
UPDATE, 3:41 p.m.: A Twitter user uploaded a video of the explosion from a local news station.
UPDATE, 3:47 p.m.: Twitter user @CaptainDurk uploaded a Vine of the finish line before the explosion...
And after the explosion.
UPDATE, 3:50 p.m.: Reports of secondary devices.
UPDATE, 3:57 p.m.: The Boston Marathon has posted a statement on its Facebook page.
UPDATE, 4:05 p.m.: Boston Police Department spokesperson Cheryl Fiandaca confirms 22 injured, 2 dead.
UPDATE, 4:08 p.m.: Boston Police department now reports 23 injuries, 2 dead.
UPDATE, 4:19 p.m.: The FAA has issued a temporary flight restriction extending in a 3-mile radius over the site of the explosion.
Boston Logan Airport remains open.
UPDATE, 4:26 p.m.: NBC News reports that a homemade bomb is the cause of the explosion.
UPDATE, 4:28 p.m.: Associated Press reports that 2 more explosives have been found.
UPDATE, 4:30 p.m.: Eyewitnesses report an increased police presence in New York City's Times Square.
Earlier, the NYPD tweeted that they would be stepping up security at prominent locations.
BuzzFeed's Ruby Cramer spoke with an NYPD spokesperson, who reported that there have been no known threats to NYC.
UPDATE, 4:37 p.m.: Reuters confirms earlier reports of an explosion at the JFK Library. AP is reporting the explosion as well.
UPDATE, 4:45 p.m.: Eyewitness report of the explosion.
Via BuzzFeed's Ruby Cramer:
Lindsay Parry, 35, lives in South Africa, works at Victoria University; visiting Boston with his wife and three friends for the marathon
Finished at 2:47, more than an hour before the attacks
He was 400 meters away from where the first explosion when off — at a pub with his three friends and wife in the Lennox Hotel on the first floor
"The cops and the police and the actual marshals of the race were incredibly efficient. They tore down all the barriers and ripped the advertising off the barriers to see if they could find any more explosions. Immediately, the medics started wheeling people off.
"When we left the hotel after 10 or 15 minutes, we walked out on the street to go back to our hotel [Liberty Hotel, a few blocks away], and there were people who weren't even aware that the explosion had happened — people in restaurants, having coffee and laughing."
"We saw people who were being wheeled out, but by that stage we hadn't seen anybody lying or injured on the floor. I didn't see anyone who I was certain was dead."
UPDATE, 4:49 p.m.: CBS reports that a man carrying backpacks was seen on a surveillance camera before the explosions.
UPDATE, 4:52 p.m.: BuzzFeed's Michael Rusch uncovers video of the second explosion.
UPDATE, 4:57 p.m.: The FAA has stopped all flights to Boston Logan airport.
UPDATE, 5:00 p.m.: Boston Police Department reports two initial explosions at the marathon finish line, third explosion under investigation.
UPDATE, 5:07 p.m.: The Red Cross has launched a searchable "Safe and Well" database so people can find out if their loved ones are OK.
UPDATE, 5:13 p.m.: Google has also set up a person finder system to help people affected get in touch with one another.
UPDATE, 5:18 p.m.: Cell phone service reportedly shut down in Boston to prevent remote detonations of explosives.
Associated Press reports:
A law enforcement official says cellphone service has been shut down in the Boston area to prevent any potential remote detonations of explosives.
Authorities have not identified what caused the explosives that erupted at the finish line of the Boston Marathon. The official was speaking on condition of anonymity because the investigation was ongoing.
UPDATE, 5:20 p.m.: Ground stop has been lifted at Boston's Logan Airport.
UPDATE, 5:25 p.m.: Approximately 75% of the Boston Marathon runners crossed the finish line.
UPDATE, 5:27 p.m.: The White House Flickr account has posted a photo of President Obama receiving an update of the situation in Boston.
UPDATE, 5:33 p.m.: NBC News reports that Boston Police have a "possible suspect" in custody.
UPDATE, 5:43 p.m.: At least 90 people are now reported to be injured. Still only two deaths.
UPDATE, 5:46 p.m.: President Obama to address the nation at 6:10 p.m.
UPDATE, 5:55 p.m.: A college reporter has posted photos of Boston police detaining a man on the Boston Common.
UPDATE, 6:03 p.m.: Marathon bombing suspect is NOT in police custody.
UPDATE, 6:08 p.m.: A 3-year-old child is among those injured, according to a local reporter.
UPDATE, 6:13 p.m.: Cell phone service in Boston in operation, experiencing heavy traffic.
WASHINGTON (AP) — Cellphone companies say service is operating in the Boston area, but with heavy traffic following of the explosions at the Boston Marathon.
A law enforcement official, citing an intelligence briefing, said cellphone service had been shut down Monday in the Boston area to prevent any potential remote detonations of explosives.
But officials with Verizon Wireless and Sprint Nextel said there had been no such requests.
Sprint spokeswoman Crystal Davis said: "Minus some mild call blocking on our Boston network due to increased traffic, our service is operating normally."
UPDATE, 6:17 p.m.: Capitol flags to be lowered to half-staff out of respect for the Boston Marathon explosion victims.
UPDATE, 6:22 p.m.: Washington, D.C., mayor reports that the city has not received any specific threats.
UPDATE, 6:28 p.m.: Video of President Obama's address to the nation.
UPDATE, 6:30 p.m.: Transcript of President Obama's remarks:
Good afternoon, everybody. Earlier today I was briefed by my homeland security team on the events in Boston. We're continuing to monitor and respond to the situation as it unfolds and I've directed the full resources of the Federal Government to help State and local authorities protect our people, increase security around the United States as necessary and investigate what happened.
The American people will say a prayer for Boston tonight and Michelle and I send our deepest thoughts and prayers to the families of the victims in the wake of this senseless loss. We don't yet have all the answers but we do know that multiple people have been wounded, some gravely, in explosions at the Boston Marathon.
I've spoken to FBI director Mueller, and Secretary of Homeland Security Napolitano, and they're mobilizing the appropriate resources to investigate and to respond. I've updated leaders of Congress in both parties, and we reaffirmed that on days like this, there are no Republicans or Democrats; we are Americans, united in concern for our fellow citizens.
I've also spoken with the Governor Patrick and mayor Menino and made it clear they have every single federal resource necessary to care for the victims and counsel the families and above all, I made clear to them that all Americans stand with the people of Boston. Boston police, fire fighters and first responders as well as the National Guard responded heroically and continue to do so as we speak. It's a reminder that so many Americans serve and sacrifice on our behalf every single day without regard to their own safety, in dangerous and difficult circumstances and we salute all those who assisted in responding to quickly and professionally to this tragedy.
We still do not know who did this or why and people shouldn't jump to conclusions before we have all the facts. But, make no mistake, we will get to the bottom of this and we will find out who did this, we will find out who did this, we will find out why they did this. Any responsible individuals, any responsible groups will feel the full weight of justice.
Today is a holiday in Massachusetts, Patriots Day, it's a day that celebrates the free and fiercely independent spirit that this great American city of Boston has reflected from the earliest days of our nation and it's a day that draws the world to Boston's streets in a spirit of friendly competition.
Boston is a tough and resilient town, so are its people, I'm supremely confident that Bostonians will pull together, take care of each other and move forward as one proud city and as they do the American people will be with them every single step of the way. You should anticipate that as we get more information our teams will provide you briefings. We're still in the investigation stage at this point but I just want to reiterate we will find out who did this and we will hold them accountable. Thank you very much.
UPDATE, 6:36 p.m.: An 8-year-old was one of the two people killed in the Boston Marathon explosion.
UPDATE, 6:42 p.m.: Boston PD and JFK Library confirm that earlier "explosion" at the library was actually a mechanical room fire.
UPDATE, 6:49 p.m.: NBC News reports that a young person in the country on a student visa is being questioned.
UPDATE, 7:00 p.m.: ABC News reports that the twin explosions at the Boston Marathon were triggered by remote detonation.
According to law enforcement sources, the first bomb exploded at the Marathon Sports running store, and blew out windows in four nearby buildings, injuring 15 to 20 individuals. The second blast occurred about 50 to 100 yards away, severely injuring more bystanders, Boston Police Commissioner Edward Davis said.
Authorities believe they were caused by small portable devices, sources told ABC News. More than 400 National Guardsmen in attendance at the marathon helped secure a perimeter around the scene.