"We like to take them down one brick at a time," but that didn't happen in this case, he said. "It's a dangerous demolition job."
Neighbor Bruce Goodman said he felt vibrations all week long while the work was underway, and rushed outside as he heard the building collapse.
"I'm stunned," he said. "It's incredible nobody's been hurt."
Officials from the Department of Licenses and Inspections were at the scene Thursday and have been all week, workers said.
L&I deemed the property "imminently dangerous" Jan. 24, and the owners obtained a demolition permit a week later, Commissioner Carlton Williams said Thursday. Demolition began Feb. 24.
"We took every safety precaution in accordance to the mayor's executive order and the new demolition legislation," Williams said at a Thursday news conference. "This was a controlled demolition. ... In the event something would happen, all protections would be properly in place."
The developer - represented by Leo Addimando of Alterra Property Group - said that as demolition crews tried to remove the top two floors of 257 Market St., a portion of that 4½-story building "buckled" and fell into 259 Market.
"That building then crumbled under the weight of the debris from above, fell through the sidewalk protection, and probably went a third of the way onto Third Street," he said.
The early-19th century row of buildings was once the site of a neighborhood landmark called the Shirt Corner and then the Shirt Corner Plus. City officials ordered the developer who was renovating the buildings to demolish them after engineers discovered wide cracks in the walls.
Alterra had planned to renovate and reconstruct the buildings to accommodate 59 apartments and a CVS drugstore.
Addimando said last month that he was disappointed by the demolition order, but would abide by the decision.
The structural problems were discovered in mid-January when workers peeled away drywall to prepare for renovations. After Addimando's engineering firm, Cooke Brown, pointed out cracks and bulges in the front facades, he sought an assessment from two engineering consultants, Keast & Hood and O'Donnell & Naccarato.
A report issued by Keast & Hood concluded that the buildings were unstable and advised that they be taken down.
On Thursday, Patricia Krup of Port Richmond was running an errand at the Federal Express store across the street when "the building just collapsed right in front of me," she said.
"I came out of the Federal Express building, and everyone started yelling, and I saw a big plume of smoke. It was all black, you couldn't see anything, and then all of a sudden the smoke cleared, and I looked to see, and I yelled to one of the guys, 'Is everyone OK?' and they said, 'Yes, everyone's OK.'
"Then I saw the bricks all over the place, and a couple of the bricks hit my car."
At the scene, David Neff of Neff Associates, a public-relations firm representing the owners, distributed a news release titled "Building Did Not Collapse in Old City."
The release called the event "a controlled and carefully planned demolition."
A security camera at the Fox29 studios at Fourth and Market captured the collapse from a distance, showing people hurrying away and a car suddenly making a U-turn on Market Street to avoid the cloud of dirt and dust.
The scene evoked memories of June 5, 2013, when a building under demolition collapsed onto the Salvation Army thrift store at 22d and Market Streets, trapping people in the rubble. Six died, and 14 others were injured.
Wayne Dunlop, a representative of Constructure, said Thursday: "Unfortunately, the worst case did happen, a collapse did occur. But it was a controlled collapse."
On Thursday, Gary Ginsberg, owner of Suit Corner across the street, was measuring a customer when he heard a boom. He went to the door and saw the rising dust and smoke.
For almost 50 years, until 2009, his uncle Marvin Ginsberg owned Shirt Corner, and his father, Jerry Ginsberg, owned Suit Corner. Along with Regent Shoes down the street, they formed the heart of Old City's discount haberdashery district.
The Shirt Corner was famous for its red, white, and blue sign and even flashier $99 suits.
"Krass Bros. may have had the crazy commercials, but Shirt Corner had divine devotion from lawyers and laborers, prom-going teenagers, twenty-something swing dancers, and grown men trying to outdress the dude in the next pew at church," Inquirer columnist Monica Yant Kinney wrote in 2009, when Marvin Ginsberg closed Shirt Corner.
The buildings, which lined the north side of Market Street, had been deteriorating for years. They once served as warehouses and offices for shipping firms.
Gary Ginsberg said Thursday that the city was initially reluctant to take down the building because of its age and historic standing, "but then they realized they couldn't restore it because it would collapse, so they did the right thing."
He said construction workers had prepared for the possibility that the building could fall, surrounding it with fencing.
"They knew something could happen, and they were protecting the area," he said. "They did everything that they were supposed to do so no one would get hurt. It was a job done correctly."
Inquirer staff writers Dylan Purcell and Joseph A. Gambardello contributed to this article.