A vacant one-story building came crashing down onto a bus stop along Broadway between 99th and 100th streets yesterday morning, briefly trapping at least four people, including a 7-month-old girl, under a pile of debris and halting subway service on the nos. 1, 2, and 3 lines. There were conflicting reports about the status of the collapse victims, but the city’s fire commissioner, Nicholas Scoppetta, said all were in stable condition.

A 25-year-old plumber, Julian Jimenez, said that when he arrived at the scene just seconds after the collapse, two women were pinned down by the rubble and had blood trickling from their foreheads. One of them shouted, “Help my baby, help my baby.” Mr. Jimenez said he soon discovered that a stroller had been almost completely submerged by the debris. He said he cleared bricks off the stroller and found a baby who was bleeding from her nose and appeared to be unconscious.

Mr. Scoppetta said one man’s arms and legs were broken in the accident, although officials at the hospitals where victims were treated, Harlem and St. Luke’s-Roosevelt, could not provide an update on the man’s status. The 7-month-old girl and the two 56-year-old women who were pinned down by the rubble spent last night at St. Luke’s, according to a hospital spokesman, Jim Mandler. One of the women, the infant’s nanny, was scheduled to undergo surgery last night. The other woman and the infant are expected to be released today, Mr. Mandler said.

In all, five pedestrians and four firemen were hospitalized in connection with yesterday’s accident, according to a firefighter who handled press inquiries for the department, Adrian Deronja of Ladder Company 12. Mr. Mandler said three firemen were treated at St. Luke’s and were released yesterday afternoon. Mr. Scoppetta said that none of the two-dozen construction workers at the site was injured.

Extell Development Company owns the collapsed building, formerly a Gristedes supermarket. Demolition crews had been working at the site for a week to make room for a planned 31-story glass apartment tower. Mr. Scoppetta said the front wall of the building crumbled, probably due to duress from a heavy piece of equipment on the roof, shortly before 9:25 a.m., taking the scaffolding down with it. Ladder Company 22 arrived at the scene within four minutes, Mr. Scoppetta said. Within a half hour, the American Red Cross had dispatched 15 relief workers to the accident site.

A freelance personal computer repairman who lives on the Upper West Side, Wesley Rivera, 43, was waiting to get a job application at a cinema across the street from the construction site, Metro Theater, at the time of the collapse. Mr. Rivera, who said he was just blocks from ground zero on September 11, 2001,said that the “rumbling noise” made by the collapsing building reminded him of the sound of the north tower at the World Trade Center falling. He said he made a running dash toward 98th street to avoid the bricks that cascaded onto Broadway’s southbound lanes.

The commissioner of the Office of Emergency Management, Joseph Bruno, joining Mr. Scoppetta at the scene, said he had halted the subway lines running under Broadway to avoid causing vibrations that could jostle the few fragments of the building’s walls that remained standing after the collapse.

At 9:37 a.m., the no. 1 line shut down from Midtown through Harlem and the no. 3 line was suspended as far south as Chambers Street about a half-hour later, according to a spokesman for New York City Transit, Charles Seaton. The no. 2 line was rerouted to the East Side and passengers were advised to take the A, B, C, and D trains, Mr. Seaton said.

That message spread slowly through the vast subterranean transit system. A 28-year-old Forest Hills man, Aaron Oeser, a construction supervisor who was riding the no. 1 train en route to a worksite on West 86th Street, said that he waited on a stalled subway car under the Port Authority terminal for about 15 minutes. “Nobody knew what was going on,” he said.

Shortly after noon, subway cars had begun to chug along at full speed, with the exception of the southbound no. 1 train, which runs directly under the site of the collapsed building. As of yesterday evening, the no. 1 train was still operating at a reduced speed of 10 miles an hour between 96th and 110th streets, Mr. Seaton said.

As ordinary New Yorkers coped with transit woes, politicians quickly converged at the site of the accident. The first elected official on the scene, a City Council member whose district includes the site of the collapsed building, William Perkins, said the building conditions “were clearly dangerous.” About 90 minutes after the collapse, Mr. Perkins, pointing to the rubble just steps away, told The New York Sun:

“This was obviously a disaster that was waiting to happen.”

On Wednesday night, Mr. Perkins participated in a rally in front of the vacant supermarket criticizing Extell’s plans for pricey high-rise apartment towers on both sides of the street. “The hundreds of people who were here with me last night, but for the grace of God, could have been amongst those injured today,” Mr. Perkins said. He is leaving the council at the end of this year due to term limits and is a candidate for public advocate.

Just 40 minutes before the building collapsed, the state Senate minority leader, David Paterson, in whose district the accident occurred, and a Democratic candidate for the council seat that Mr. Perkins is vacating, Inez Dick ens, led a procession of volunteers underneath the construction site scaffolding as they collected signatures on a petition opposing Extell’s plans, according to a Paterson aide, Shammeik Barat.

Also at the scene, a Democratic assemblyman from Harlem, Keith Wright, said he thought the demolition company, Safeway Environmental Corporation of the Bronx, and Extell were “quite possibly negligent.” Mr. Wright told the Sun: “Hopefully, this was just a tragic accident. But buildings get taken down every day without babies being hurt.”

There was no evidence yesterday that Safeway Environmental had violated any city codes. The city’s building commissioner, Patricia Lancaster, said Extell and Safeway had obtained all necessary permits. Still, Ms. Lancaster ordered a halt to construction activity at the site and at the Extell-owned property across the street, pending her office’s completion of an investigation into the causes of yesterday’s collapse.

Safeway officials declined to comment yesterday, referring all inquiries to a spokesman for Extell, Robert Liff. In a statement yesterday, Mr. Liff said Safeway is “one of the city’s premier union demolition companies with a long record of safe performance.”

A 34-year-old woman, Norma Santos, who lives about a dozen blocks north of the site of the collapse, said that she had shopped at the Gristedes supermarket before it closed and remembered that the building was “not in good condition.”

Ms. Santos said she remembered seeing a rat emerge from a hole in the floor of the dairy aisle. She also recalled seeing rain trickling through a leak in the ceiling about seven months ago when she peeked into a storage closet at the supermarket.