8:58 p.m. EST: Death toll at 3; more than 130 injured with 17 in critical condition and 9 in surgery per CNN.
7:08 p.m. EST: CultureMap Austin contributor Matt McGinnis is currently in Boston, supporting his wife who ran the Boston Marathon. He offered his account of the bombings, which are now being called a terror attack. It's currently unknown if the event was perpetrated by a domestic or international group or individual.
7:05 p.m. EST, injured count up to 110, including children.
At 4:55 p.m. EST, police confirmed a third explosion at JFK Library, which is under investigation.
Business Insider says New York Police Department are stepping up counter-terrorism vehicles around Manhattan. Family members are being asked to call 617-635-4500. The Red Cross is accepting cash donations and blood donations.
At 4:19 p.m. EST, amount injured and being treated at Mass General rises to 28.
As of 4:02 p.m. EST, 23 are reported injured and two dead. Those numbers are expected to rise. To locate friends and family participating in the marathon, you can look up where runners last checked in online. WCVB Boston says victims were being taken to Massachusetts General Hospital.
At 3:30 p.m. EST, The Associated Press reported, “About three hours after the winners crossed the line, there was a loud explosion on the north side of Boylston Street, just before the photo bridge that marks the finish line. Another thunderous explosion could be heard a few seconds later.”
The Boston Globe official Twitter account is delivering a steady stream of real-time updates from the 117th Boston Marathon, including "[A] cook I talked to says he tied his apron around a woman's severed leg" and "Finish line volunteers told to run. Describe fear like 9/11 or the tsunami."
The Chicago Tribune reports "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."
Two explosions were confirmed to have been controlled devices and took place less than half a mile apart, across from the Lenox Hotel. The race, which hosts nearly 27,000 runners, was stopped as athletes neared an underpass in the Back Bay. All off duty Boston police officers have now been called to the scene.
As the marathon kicked off this morning, NPR ran a report on runners from Newtown, Connecticut who said they were running each mile of the marathon in memory of the 26 victims of the December 14 Sandy Hook Elementary massacre.
"The race day got started with 26 seconds of silence in honor of the victims of the Sandy Hook Elementary School shooting." The Mile 26 marker was decorated with the Newtown seal and "dedicated to the memory of those killed there."
Washington, D.C. is on high alert. The source of the bombing is not yet confirmed.
Keep up with CNN's live blog here.
**Below is a clip of the explosion.
Viewer discretion advised.**