(CNN) -- Equipped with search cameras, microphones and motion detectors, and bathed in harsh LED lights that illuminated the darkness, rescue workers combed through piles of bricks and rubble early Thursday, listening for the faint tap-tap-tapping of life buried in the ruins of a collapsed building.
Search-and-rescue workers have covered about 75% of the site of Wednesday's building collapse in Philadelphia, Mayor Michael Nutter told reporters Thursday morning. Searches of the the rest of the site continues, he said.
A day earlier, the side of a building under demolition had given way and toppled onto a Salvation Army thrift store next door.
Throughout the day Wednesday, dispirited emergency responders had carried out six people in body bags. But they received a momentary jolt of joy when, shortly before midnight, they pulled out 61-year-old Myra Plekam alive.
She was the 14th survivor.
"It feels outstanding to be able to pull somebody (out) alive," the city public safety spokesman Michael Resnick said.
Philadelphia Mayor Michael Nutter told reporters late Wednesday night that authorities didn't know many people were in the store at the time of the accident.
He was concerned the collapsing wall may have also hit people walking by outside.
More than a third of the rubble still needed combing through, Fire Commissioner Lloyd Ayers said.
And so responders searched on. Slowly. Carefully.
Empty dump trucks came -- and left with their buckets filled with cleared debris. More arrived.
Crashing sound, shaking earth
Boskie Shah had stopped to watch the demolition work just before the side of the building fell over around 10:40 a.m. ET Wednesday.
A construction crane bumped the building twice, before it swayed, he said.
"The right wall leaned toward 22nd St and collapsed on the thrift shop."
Debris spread out, and a dust cloud rose through the air. Shah took a photo and later uploaded it to CNN iReport.
Jordan McLaughlin felt the earth shake under his feet when the wall landed on top of the thrift store, he told CNN affiliate KYW.
"There was people that actually fell over," he said. "People started screaming, they ran across the street. There was people inside the building, you heard them scream."
He said he helped two people out of the building. Other bystanders, including construction workers, helped four or five others out.
Another witness, Ari Barker, said he was in his office across the street when he heard "a rumbling, a very unusual sound." He rushed to the window to see a plume of dust rising from the debris.
Some saw it coming
"I knew that was going to collapse sometime soon, and it did today," Patrick Glynn told CNN affiliate WPVI.
"For weeks, they've been standing on the edge, knocking bricks off, pieces off, you could just see it was ready to go at any time. I knew it was going to happen. I seen it. I said it 10 times. Ask these guys. Every day, I said, 'It's gonna collapse, it's gonna collapse.'"
Minerva Pinto works nearby. She and her coworkers thought the building looked precarious in the days before the collapse.
"We'd all seen in the past week that the building was really unstable because of the demolition," she told CNN's iReport.
But city officials said there were no known violations at the site.
"No violations, no complaints that we're aware of, and all permits were valid," Nutter told reporters earlier.
Focused on tragedy
When reporters pressed him again with questions about required inspections of the demolition work during a nighttime news conference Wednesday, Nutter appeared irritated,
"There's a full investigation that will be conducted by the department of license and inspections," he said.
He said he was focused on the immediate calamity and the human tragedy it had wrought.
"We've lost six lives today. Think about that," he said. "We've actually spent most of our time today trying to see if anyone is still alive."
Nutter asked journalists not to reveal the names of the dead.
"Family members have lost a loved one. All of those families deserve to be notified by their family members rather than hearing about it on television or the radio or the Internet or the newspaper," he said.