Watch video of the explosions near the Boston Marathon finish line.
Southern California residents who participated in Monday's Boston Marathon described the horror and chaos that ensued when two explosions went off at the finish line, killing two people and wounding at least 100.
Nancy Jo Rettig, of Redondo Beach, was running with a group called Loopsters when she heard the explosions.
“We were walking towards the tunnel,” she said from her cellphone as she and her group walked back to a houseboat in the harbor where they were staying. “You could smell it in the air.”
She said chaos ensued as police checked their radios and began ordering people out of the area. She said transit was shut down immediately and runners were ordered out of the tunnel.
"I just crossed the finish line and heard an explosion and didn't know what it was," said Grace Kim, a runner who was in Boston with the Cerritos-based "Easy Runners" club.
"It sounded louder than fireworks," Kim said.
As the news developed, Southern California law enforcement agencies began the process of expanding security as a precaution against the potential for a similar attack here.
The Los Angeles County Sheriff's Department and Los Angeles Police Department added extra patrols.
The added Sheriff's Department patrols focused on public transit, places where people congregate and government buildings, said department spokesman Steve Whitmore. The Metropolitan Transportation Authority also announced increased security measures and additional inspections of the bus and rail system.
Orange County authorities took similar precautions by beefing up police presence in public gathering places and sporting venues, Orange County Sheriff Sandra Hutchens said.
Organizers for the Orange County Marathon on May 5 are consulting with regional law enforcement to ensure the safety of participants and audience members, said Gary Kurtscher, race director for the event. He said organizers are waiting to learn more about the explosions in Boston before making any major decisions.
Officials hosting the Toyota Grand Prix of Long Beach this weekend said they were also adding security as a precaution.
Meanwhile, social media sites were abuzz with first-person accounts of the explosions and updates about participants' welfare. Google has launched a person finder to help find people who were at the Boston Marathon or to report information on people who were there.
Southern California running groups used websites such as Facebook and Twitter to confirm their members at the Boston Marathon were safe.
The L.A. Leggers running club posted a Facebook message attributed to member Jennifer Hartman saying she was 20 yards from the finish line when the bomb went off.
"We saw it all," the post said. "We turned around and were going to go back when the explosion behind us occurred. At that point we stood in the middle for a moment holding hands and wondering if any more explosions were going to happen."
Culver said that judging by the unaccounted-for members' previous finish times, they probably would have finished long before the explosion occurred. One runner, however, was slowed down by an injury and finished four minutes after the explosion.
"I believe they're going to be fine," Culver said. "We're just trying to piece it together."
Kevin LaBeach contributed to this report.
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