Around 3 p.m. on Monday, Maria Vargas was in her daughter’s room on the third floor of their Bronx apartment building when cracks shot across the walls.

One wall was split down the middle. Ms. Vargas, 55, whose husband is the building’s superintendent, joined a mob racing for the exit. Then the entire corner of the building crashed down, sending jolts through the neighborhood and spilling the innards of several homes.

“I thought to myself,” Ms. Vargas said, “‘Oh my God, I’m going to die.’”

“I haven’t slept,” she added. “Every time I close my eyes, all I see is the crumbling room.”

No one was killed or severely injured in the partial collapse of the 46-unit building in Morris Heights. A day later, officials offered few conclusions, saying that the incident was under investigation.

The collapse shed a brighter light on the limited oversight of aging infrastructure, especially after the fatal collapse of a Manhattan parking garage in the spring and the disaster at a condo building in Florida in 2021.

Before the Bronx collapse, residents had complained of numerous problems, including issues with the facade that had not yet been fixed, city building records showed.

Miriam Rodriguez, 63, said she has lived in the building for 30 years and had previously called the city with complaints.

“All sorts of things could be fixed, from the floors to the ceiling,” she said, adding, “There was a crack in the walls on the outside corner that collapsed. It got wider and wider and no one ever did anything about it.”

Abi Aghayere, a civil engineering professor at Drexel University who studies structure failures, said he did not believe the city’s oversight of buildings was sufficient.

He said regulators tend to pay closer attention before and during construction or when an owner is seeking permits. After that, the onus to identify and fix problems is almost always on the owner, he said, adding that New Yorkers should be worried.

“I was thinking about that yesterday,” he said, “that I could be living in that building.”

By law, a building owner must hire licensed engineers and contractors to do periodic inspections. Retaining walls, for example, must be inspected every five years. Boilers must be inspected annually. City inspectors might also respond to residents’ complaints or conduct surprise inspections.

Asked on Tuesday whether the city should change its policies, Mayor Eric Adams said he believed in the scheme of owners using outside, certified engineers and architects to review safety issues. But he also said the city needed to make sure the system worked correctly.

“Every collapse is a bad collapse,” he said. “Many of our buildings come from an older stock. You have this from time to time.”

Officials with the Buildings and Housing Departments said they were not aware of any warning signs that could have predicted the crash. The Bronx District Attorney’s office said it was looking into the collapse.

Richard Koenigsberg, an engineer overseeing repairs to the building’s brick facade, said a contractor had been at the site on Monday, but that no work had been done in the area of the collapse in the last month.

The facade was not merely ornamental but was bearing part of the weight of the 96-year-old building, as is common in tenements of that vintage, he said.

Mr. Koenigsberg said he would not speculate about the cause of the collapse. But he said it “isn’t a facade collapse,” adding, “I strongly suspect it was a catastrophic collapse of the structural column in the corner of the building.”

Mr. Koenigsberg said he met on Tuesday with Buildings Department officials and was cooperating with their investigation.

Mr. Koenigsberg, who has been inspecting building facades in the city and overseeing their repair for more than 30 years, said the collapse was not foreseeable. In the context of the 1998 local law that requires periodic inspections of facades, he said, “this is a very rare type of failure.”

He had declared the facade unsafe in 2020 to signal that a sidewalk shed was needed to protect pedestrians during repairs. That work was delayed by the pandemic, but he said the collapse was “certainly not foreseeable as a result of not doing the work” sooner.

Whether and when to conduct repairs would have been up to the building’s owner, which city records showed to be a limited liability company, 1915 Realty. The man listed as the principal of that company, David Kleiner, could not be reached for comment on Tuesday.

Outside the relief center set up for the building’s residents at Bronx Community College, a spokeswoman for the American Red Cross, Desiree Ramos Reiner, said the group was trying to place 146 members of 46 households across the city.

Ms. Vargas’s daughter Sharlene, 23, a pharmacy technician, said that Monday was supposed to be her day off. Usually, she spends it resting and cleaning her bedroom, which she shares with her 2-year-old daughter. Instead, she picked up an extra shift, which she rarely does.

“I hear that this happens,” she said, “and I just feel, I don’t know, shocked.”

Her bedroom is on the ground now.

“You can see my daughter’s jacket hanging in the room,” she said. All the Christmas gifts she bought are in the rubble, including a Build-a-Bear stuffed animal for her daughter.