UPDATED 4:45 p.m.
Two bombs exploded near the finish line of the Boston Marathon on Monday, killing two people, injuring 23 others and sending authorities rushing to aid wounded spectators. A senior U.S. intelligence official said two other explosive devices were found nearby.
Competitors and race organizers were crying as they fled the chaos. Bloody spectators were being carried to the medical tent that had been set up to care for fatigued runners.
"There are a lot of people down," said one man, whose bib No. 17528 identified him as Frank Deruyter of North Carolina. He was not injured, but marathon workers were carrying one woman, who did not appear to be a runner, to the medical area. A Boston police officer was wheeled from the course with a leg injury that was bleeding.
At least half dozen people were injured, based on photos of the scene appearing on Twitter.
Shortly before 3 p.m., 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.
Runner Laura McLean of Toronto said she heard two explosions outside the medical tent.
"There are people who are really, really bloody," McLean said. "They were pulling them into the medical tent."
Cherie Falgoust was waiting for her husband, who was running the race.
"I was expecting my husband any minute," she said. "I don't know what this building is ... it just blew. Just a big bomb, a loud boom, and then glass everywhere. Something hit my head. I don't know what it was. I just ducked."
Based on photos, the second explosion may have been on the sidewalk near the finish line.
Andrew Katz, a Time magazine reporter, tweeted that a Boston EMS scanner is reporting another unexploded device in front of the Mandarin Hotel on Boylston Street.
For the top runners, the Boston Marathon had ended about two hours prior to the explosion. But there were an estimated 27,000 participates, and many had not yet crossed the finish line.
The race has been halted and the Boston Marathon media center has been locked.
Copyright 2013 The Associated Press.