[UPDATES BELOW] There's been an explosion near the finish line of the Boston Marathon on Boylston Street today. According to initial reports, multiple people are injured.

The winners had passed by several hours before the explosions occurred at approximately 2:50 p.m., which is about the time when a large influx of runners who finish within four hours arrive. ABC is reporting that at least a dozen people were injured.

Update 3:16 p.m.:Here's the view from the finish line camera. “I saw two explosions," says Boston Herald reporter Chris Cassidy, who was running in the marathon. "The first one was beyond the finish line. I heard a loud bang and I saw smoke rising,” “I kept running and I heard behind me a loud bang. It looked like it was in a trash can or something. That one was in front of Abe and Louie’s. There are people who have been hit with debris, people with bloody foreheads.”

Here's another, more graphic photo.

The marathon began earlier this morning with a series of staggered starts: 9:17 a.m. was the Push Rim Wheelchair division start; the Elite Women's group started at 9:32 while the Elite Men's group started at 10 a.m. with Wave One; Wave Two started at 10:20; and Wave Three started at 10:40 a.m.

Update 3:28 p.m.:WBZ-TV reports that some victims lost limbs and there is "a lot of blood" at the scene. At least ten people taken away from the scene on stretchers.

Update 3:42 p.m.: Here's video of the explosions:

Update 3:45 p.m.: There's been no official statement on the number of injuries and fatalities. Fox News is reporting that three people were killed, but that's not confirmed.

Update 4:08 p.m.:
The Boston Police Department has announced via Twitter that 22 people were injured and two people killed. It appears that most of the victims were spectators, not runners.

Update 4:14 p.m.: ABC reports that Boston police set off a controlled explosion along the marathon route. The Mandarin Hotel, up the street from the finish line, has been evacuated, as has the Lenox Hotel, about 150 yards from the finish line. The Boston Fire Department will be holding a press conference at 4:30.

Update 4:22 p.m.: An official tells ABC it is now "clear this was a bombing." The source says the explosions were caused by "small, multiple portable devices."

Update 4:34 p.m.: No one has claimed responsibility for the bombing. Today is also Patriot's Day, which is widely celebrated in Massachusetts to commemorate the anniversary of the Battles of Lexington and Concord.

Update 4:46 p.m.:Sources tell the Post authorities have a suspect in custody, at a hospital with shrapnel in his leg. Here is another video of the explosion and its aftermath.

Update 4:55 p.m.: At a press conference, the Boston Fire Department Commissioner Edward David said there was a third incident: An explosion at JFK Library in Cambridge, which sparked a fire. The Commissioner said it was unclear that the incidents were connected, but officials are urging Boston residents to stay home if they're home, telling the press, "We want to completely stabilize the situation."

Victims are being hospitalized with "shrapnel-like wounds." People searching for information about loved ones are being told to call (617) 635-4500 and anyone with information is being asked to call 1-800-494-TIPS.

Update 5:10 p.m.:
Roupen Bastajian, a 35-year-old state trooper from Rhode Island, had just finished the race when the explosions occurred. "I started running toward the blast," Bastajian tells CBS. "And there were people all over the floor. We started grabbing tourniquets and started tying legs. A lot of people amputated. At least 25 to 30 people have at least one leg missing, or an ankle missing, or two legs missing."

Update 5:17 p.m.:
A law enforcement official tells the AP cellphone service has been shut down in the Boston area to prevent any potential remote detonations of explosives. The Boston Police Department press office could not confirm this.

Update 5:22 p.m.:The NY Post reports that a Saudi national be guarded by police at a Boston hospital and is suspected of involvement in the bombing. But the Boston Police Department says this bullshit. No suspects have been taken into custody, and a police spokesman tells Talking Points Memo, "Honestly, I don't know where they're getting their information from, but it didn't come from us."

Update 5:42 p.m.: A spokesperson for the Boston Police Department tells us the fire at JFK library is still under investigation. It was announced earlier that there was an explosion at the library, but the spokesperson would not confirm an explosion and according to their Twitter feed, the "incident appears to be fire related."

President Obama will address the nation at 6:10 p.m.

Update 6 p.m.:The AP is now walking back its report that cell phone service is being shut down to prevent remote detonations of explosives. Officials with Verizon Wireless and Sprint Nextel said there had been no such requests, and Sprint spokeswoman Crystal Davis said: "Minus some mild call blocking on our Boston network due to increased traffic, our service is operating normally."

Update 6:15 p.m.:In his brief televised address, President Obama said, "Boston is a tough and resilient town. So are its people." He took no questions.

Update 6:20 p.m.:
The Boston Police have now officially confirmed two fatalities. This statement was posted on their website:

At about 2:50pm, on Monday, April 15, 2013, Boston Police responded to two large explosions along the Boston Marathon route in the area of 673 Boylston Street.

The Boston Police Department is confirming two fatalities and over twenty injuries.

At about 4:12pm, the Boston Police Department responded to a 3nd explosion or fire in the area of the JFK Library in Dorchester. Officials are working to determine the nature of the incident. There are no injuries to report in connection to that incident.

At present, a multi-agency response including state and federal law enforcement agencies has been activated and is investigating the cause of the explosions. At this point, it is uncertain if the explosions are connected.

Update 6:37 p.m.

: NBC News Tweets, "Law enforcement official confirms that one of two people killed in today's explosions was eight years old. #BostonMarathon"

Update 9 p.m.: The Boston Police have confirmed that a third person died from the explosions. Police Commissioner Edward Davis said, "I offer my sympathies to the families impacted by this horrible tragedy. Those responsible will be brought to justice."

Additionally, the FBI is taking over the investigation.