As construction crews on Thursday added more temporary steel supports to a Midtown Manhattan building that had become dangerously destabilized earlier this week, a developer sought to reassure investors that it would not slow the project down.

The 37-story high-rise, the former headquarters of Pfizer, was set to be the largest conversion of offices to apartments in the United States. But on Tuesday, two columns on the 21st floor buckled, forcing the evacuation of hundreds of people in the surrounding buildings, shutting down traffic and prompting a major emergency response to keep the building from partially collapsing.

On Thursday, the New York City Department of Buildings said that construction crews had installed “temporary shoring” on every floor from the ninth floor to the underside of the roof . The department said it had also placed steel columns throughout the building to reinforce its original columns. City officials did not immediately make clear why support was added on floors beyond the initial damage.

It is not yet clear what led to the columns buckling, and the Buildings Department said it was still investigating. But Nathan Berman, the founder of MetroLoft, one of the building’s developers, has been communicating with investors since Tuesday, reassuring them that the project will be completed in 2027 on schedule, with relatively minor delays, according to two people familiar with the talks who asked not to be named because of the sensitivity of the issue.

MetroLoft on Thursday declined to comment on the talks. But a spokeswoman confirmed an earlier report by Bloomberg News that the developer plans to rebuild 15 floors of the building.

The building site was much more lively on Thursday than it had been the day before, with banging reverberating from the building’s upper floors to the street below. Men could be seen bringing in additional steel reinforcements.

The temporary hollow steel supports that were added to the site to shore up the structure appeared to be “very, very strong in compression,” said Dr. Dan Linzell, the dean of the School of Engineering at Worcester Polytechnic Institute. They are likely to hold the necessary weight until a more permanent fix is made, he said.

Dr. Linzell said replacing the compromised I-beam columns would be a delicate, tedious process.

“The shoring is used to jack up the floor around the column and take the load off the column and then remove it, and then put a new one in, and go to the next one, and do the same thing,” Dr. Linzell said. “And so, if there’s a lot of columns, again, it’s a non-trivial amount of stuff that needs to be done.”

Mr. Berman has said he expects a delay to last only a few weeks. If MetroLoft has the resources, Dr. Linzell said, that isn’t impossible.

The episode has cast a cloud over the concept of converting office buildings to housing. Such conversions, which have accelerated in recent years, have been seen by public officials and the real estate industry as a smart way to repurpose old and underused offices to deliver sorely needed housing.

In an interview on Thursday, Mark Levine, the New York City comptroller who has supported office conversions and announced plans to invest pension funds in these types of projects, acknowledged New Yorkers’ panic that came out of the incident. But he said people should not be scared of these types of projects, calling them “one of the bright spots” in the city’s approach to housing.

“We do really have to reassure the public that, ‘OK, we have figured out what went wrong here, and why,’” he said.

As light rain began to fall on Thursday, Sean Dow, a member of Steamfitters Local 638, one of two unions on the project, described the panic on Tuesday morning at a news conference across the street from the former Pfizer building.

That day, Mr. Dow said, he had been sent to the building’s 22nd floor to work on fire suppression when he noticed cracks in the concrete floor. He walked down to the 21st floor and found a group of general contractors huddled around a bent column. Mr. Dow took a picture and sent it to his foreman, and the two men decided the building needed to be evacuated.

Mr. Dow ran down the stairs to the fifth floor, where he knew some of his colleagues were working, and told them to get out of the building. Anyone he saw, he said, he told them to evacuate. The New York Times verified video from Tuesday that showed twisted and bent metal framing and a column bent so far it looked like it was about to snap.

“This is something brand-new,” Mr. Dow said in an interview before a news conference. “I’ve never seen anything like this.”