People near the finish line of the Boston Marathon described horrific scenes of the chaos that followed two loud explosions in quick succession this afternoon, sending spectators rushing away from the scene in panic as others lay bloodied and wounded on the ground.
One witness, Aaron Michael told member station WGBH that he heard first one explosion and then another.
"Boom, there was black smoke," he said. "Mass chaos. I saw one woman really, really badly hurt. She was being carried out by people, she was bleeding pretty badly. It wasn't a good scene. It was awful."
WGBH's Anne Mostue said she heard two very loud explosions, and then immediately saw "people screaming and running toward the river."
Running in the marathon was Boston Herald reporter Chris Cassidy, who said he heard two explosions: "The first one was beyond the finish line. I heard a loud bang and I saw smoke rising.
"I kept running and I heard a loud bang. It looked like it was in a trash can or something," Cassidy said. "There are people who have been hit with debris, people with bloody foreheads."
With thousands gathered to cheer on the runners, many took to Twitter and other social media to describe the shocking violence.
The Boston Globe's David Abel, who has reported from war zones in the past, was at the finish line filming runners when the explosions struck. He described what followed as "the worst thing I've ever seen in my life.
"There were people lying on the ground, mangled blood, glass shattered," he said. "It was really chaos."
"People missing limbs, and it appeared that the blast shattered windows," he said.
Abel said it took about 10 minutes to start getting the wounded away from the scene. The video he filmed presents more than two and a half minutes of the chaotic scene, as police, rescue workers and passersby all work to pull temporary fences away and reach the wounded.
Those injured included children, Abel said, and first responders "treated dozens of people with trauma ... they were stabilized and put on ambulances."
Jackie Bruno, a reporter for New England Cable News, tweeted: "Runners were coming in and saw unspeakable horror." She also posted a photograph showing one man lying on the ground, blood all over his legs.
Timothy Quinlan, a volunteer security officer told NPR's Adam Davidson that the first explosion as loud as a cannon came from ground level, and that he had seen dead bodies and body parts amid the debris. He said he did not see any of the runners injured.
Bruce Gellerman, a reporter with NPR member station WBUR in Boston, said that "scores and scores of ambulances" were on the scene and that everyone, including reporters, was being pushed away from the scene of the explosions.
There are "people crying, people sitting collecting their thoughts. Some of the runners are still shaking," Gellerman said about an hour after the explosions.
The Associated Press quoted one woman as saying she was waiting for her husband to cross the finish line and, in her words, "It just blew." She said the explosion was "a loud boom, and then glass everywhere."
Cherie Falgoust told the AP that something hit her in the head and she "just ducked," while runner Laura McLean of Toronto described people who were "really, really bloody."