First explosion captured on BBC video

UPDATE 2:50 p.m.

Though police counts remain at 23 injured, local hospitals are reporting at least 46 patients due to the explosions. The Boston Globe is reporting 100 injuries.

UPDATE 2:20 p.m.

Authorities reported a third explosion at the John F. Kennedy Library, elsewhere in the city, more than an hour after the blasts. There were no immediate reports of injuries. Police are now addressing it as a fire-related issue and not connected to the previous explosions, according to local media outlets. The police commissioner urged people in Boston to stay inside.

ORIGINAL STORY

Two explosions went off near the finish line of the Boston Marathon on Monday, killing 2 and injury 23 among the runners and spectators. The blasts were described by race organizers as two bombs. A third explosive device was discovered and set off in a controlled explosion by law enforcement officials.

Video from the finish line showed screams and an enormous cloud of white smoke, and about 20 seconds between the blasts. The Associated Press reported that bloody spectators were being carried to a medical tent that had been set up to care for tired runners.

Jackie Bruno, a reporter for New England Cable News, said on Twitter that she saw people’s legs blown off.

“Runners were coming in and saw unspeakable horror,” she said.

Boston Medical Center said that it had 19 patients so far, 6 in critical condition, 5 in serious condition and 8 in an unspecified condition.

NBC affiliate WHDH said that storefront windows nearby were blown out.

The race is a signature event in Boston. Race organizers said that almost 27,000 runners competed, representing 96 countries. Tens of thousands of spectators turn out each year to watch. A special marker at the 26th mile of the course, yards from the finish, had been set up to honor the 26 dead in the Newtown, Conn., elementary school shooting last December.

At least twelve athletes from the Santa Clarita Valley were participating in the race:

* Gerald Jones, Canyon County

* Zack Totten, Canyon Country

* Elaine Woodward, Canyon County

* Hoshang Dubash, Valencia

* Angela Reynolds, Valencia

* Steven Loy, Valencia

* Mara Stegemann, Valencia

* Dennis Lebman, Saugus

* David Weary, Acton

* Jodi Broz, Stevenson Ranch

* Wayne Lee, Stevenson Ranch

* Jana Whatley, Agua Dulce

The race began at 10 a.m., and the explosions were reported just before 3 p.m. The winners had long ago completed the race, but the explosions came as masses of other runners were approaching the finish.

Will Ritter, the spokesman for Massachusetts Senate candidate Gabriel Gomez, told NBC News that he heard what sounded like two explosions and saw smoke rising near the Boston Public Library. He said that he saw three fire engines and police running to the site.

“We heard two really large explosions in rapid succession, about a second apart from each other,” Ritter said. “Everybody kind of ducked and hit the ground.”

The AP reported that runners and race organizers were crying as they fled the scene. Runners who were still on the 26.2-mile course were being stopped and directed elsewhere, the Massachusetts Emergency Management Agency said. The agency suggested that people trying to reach loved ones use text messaging because of crowded phone lines.

Federal authorities told NBC News that they had no immediate information. In New York, a spokesman told Reuters that police were deploying counterterrorism vehicles around landmarks, including prominent hotels.

Allison Pari of KHTS AM-1220 and Tracy Connor of NBC News contributed to this report.