Mayor Michelle Wu gleefully took a sledgehammer to the walls of an eight-story South Boston building to break ground on the city’s largest office-to-residential conversion project to date, accounting for 77 of the 141 such units under construction.

Wu, flanked by her planning and housing chiefs, key state elected officials, including ally Rep. Aaron Michlewitz, and developers behind the latest project, spoke to how yesterday’s milestone marking the first 100 office-to-housing units under construction seeks to make a small dent in the city’s housing crisis.

“We’re so proud that this building will now be home to 77 families, including 15 families living in income-restricted affordable units right here in Fort Point,” Wu said inside the sweltering construction site at 263 Summer St. “By the end of the summer, we will be up to more than 140 new units under construction right now through our office to residential conversion program.

“Now, I know the need is immense, and when we talk about the housing crisis in Boston and Greater Boston, it’s not just in single units,” the mayor added. “It’s not even in dozens of units or hundreds of units. We’re talking about tens of thousands of units — but every little bit makes a difference.”

While 263 Summer St — the former Boston Wharf Co. building, at 63,760 square feet — is the largest project to get going through the office-to-residential conversion program, it is by no means the first. In fact, Wu said, one such project at 281 Franklin St., is nearing completion, and will be ready to house tenants in 15 homes by the end of the summer.

The developer behind both mixed-use projects is Adam Burns, owner of Burns Realty & Investments, who said the program has allowed for a quicker permitting process that will lead to “vital housing being delivered to Boston years sooner than it otherwise would have.”

Others include 129 Portland St. in the Bulfinch Triangle, with 25 units under construction, and 615 Albany St. in the South End, where 24 homes are being built.

The city program, still in its infancy and benefiting from millions in state cash, seeks to convert vacant office buildings into new homes for residents, with an eye toward revitalizing the downtown in a post-pandemic remote-work-oriented world.

“Everybody like me in every part of the country is thinking about, how do we get people back in their offices more often?” Michael Nichols, president of the Downtown Boston Alliance, said. “It’s not free coffee. It’s not forcing people to be there on a Wednesday. The No. 1 metric across the United States for people returning to their office is the proximity they live to that job.”

Nichols expressed optimism that converting unused office space into residential units, at a time when vacant office buildings are driving down values, will “load more people into the downtown” to support small businesses, return people to offices, and thereby return value “to the traditional job center that is the downtown.”

Wu argued that the downtown revitalization is already underway, paving the way for new residents to make the area their home. Per the mayor, violent crime in the downtown has dropped 48% over the last three months, compared to the same time period last year.

Foot traffic rates are up 11% in the last four months, compared to the same period last year, Wu said. Since she took office three and a half years ago, Wu, who is up for reelection, said nearly 20 new companies have moved in or expanded downtown.

“The statistics are great right now,” Nichols agreed. “The missing piece is going to be bringing more people to live in and near the downtown. So, we are thrilled about this project.”

Kairos Shen, the city’s planning chief, acknowledged that an office-to-housing conversion is not cheap, but said the city aims to offset the cost to developers through incentives.

“Converting a building from commercial use to residential use is complicated and expensive,” Shen said. “Our program allows developers to transition the building rapidly from the commercial to residential tax base through a 75% tax abatement for 29 years on that new residential tax rate.

“Our program supports these projects and makes them financially feasible because of the enormous benefit that they will deliver to Boston and our residents.”

The city received a $15 million infusion in state cash for the program last year, to fund up to $215,000 per affordable unit with a cap of $4 million per project. Gov Maura Healey’s administration awarded another $7.4 million to help to fund two planned projects, at 31 Milk St. and 15 Court Square, last month.

The city has received 16 applications, totaling 780 new units of housing, since the program’s launch in October of 2023. Of those units, which span 21 buildings, 142 would be income-restricted.

The planning board has approved 595 of those units, and construction will begin on more than 100 additional units this fall, the mayor’s office said.

The event was not without some drama. City Councilor Ed Flynn, who represents South Boston and “worked closely” on the planned development, said he was excluded from the mayor’s press communications for the event, while other elected officials were highlighted.

Flynn said he did not attend, as a Council hearing was taking place at the same time. Councilors were at the event “in spirit,” but not in person, Wu said.

The councilor also took a swipe at the Wu administration’s approach to increasing the city’s affordable housing stock. Flynn said it is time to “prioritize the city’s future with a temporary rollback” of its inclusionary development policy, which sets aside a certain percentage of units in new developments as affordable, “to be reviewed in 3-5 years, depending on economic conditions.”

“It’s time to have the courage to finally acknowledge today’s reality,” Flynn said in a statement. “A higher percentage of affordable units may be noble and with the best of intentions to address our affordable housing crisis for working families. But, in these conditions, if we’re producing less housing, we’re also getting less affordable units for residents and families who qualify.”