The building that burned was a feared checkpoint during apartheid.

He called the tragedy unprecedented. “Johannesburg has never had an incident like this where so many people die as a result of a fire in the center of the city,” he said.

He added that the police also needed to clamp down on criminals who extort money out of the residents of these derelict dwellings.

“The lesson for us is that we’ve got to address this problem and root out those criminal elements,” he said. “It is these types of buildings that are taken over by criminals, who then levy rent on vulnerable people and families who need and want accommodation in the inner city.”

Working at what was widely known as the “pass office,” the white staff issued, checked and revoked permits that governed where Black Africans could live and work, with the aim of maintaining white dominance.

A visit to the pass office could be a protracted and humiliating experience. “The snaking line of black bodies reminded me of prisoners being searched,” the South African writer Mtutuzeli Matshoba wrote in a literary account in 1980 of a visit to the “notorious” building. “That was what 80 Albert Street was all about.”

The office received provisional protection as a heritage site in 2011.

Her group works with people who are under threat of being evicted from occupied buildings to ensure that they do not end up on the street. She said that many of them are informal vendors in the city who make only a few thousand rand a month, or less than $200, and cannot afford even the lowest rents. At the same time, they need to be near the city center to work.

After officials lifted restrictions on movement that the government imposed in the apartheid era, experts said, many lower-income people moved to the cities in search of better opportunities. But there was not enough affordable housing for the influx.

The government, rights activists say, has prioritized the building of private rental units and student accommodations, which are more profitable than the public housing for which poor residents fill long waiting lists.

“There are a lot of houses that are being built for those who can afford them,” said Thami Hukwe, the coordinator of the Housing Crisis Committee, a residents’ group in Gauteng Province, which includes Johannesburg. He said that the Black population was the most affected by the housing crisis.

“We are not being prioritized,” he added, “especially the poor and the working-class communities.”

At the same time, Ms. Bhengu said, many landlords in the late 1990s abandoned buildings in the city center, wary of the uncertainty of a new democracy. These buildings have slowly filled up with those who could not afford to live elsewhere, she said, as poorer residents found makeshift solutions the government was not providing.

“There’s a lack of political will to keep poor people in the inner city,” she said.

This year, Mr. Tshwaku started a program to inspect such buildings and work to get residents out because of the dangerous living conditions. City inspectors had recently visited the building where Thursday’s fire occurred, he said, and found conditions similar to those of other structures that are considered risky.

Many lack fire escapes, extinguishers and sprinklers, he said, and they often have no running water, electricity or working bathrooms. Residents light fires for warmth and light, and that can easily lead to deadly fires, he said.

Preliminary evidence suggests that the fire on Thursday started on the ground floor, Mr. Tshwaku said. A security gate trapped many residents who were unable to escape, he added.

The operation to clear illegal buildings has inspected 14 of them, Mr. Tshwaku said. One challenge, he said, is that the city lacks the resources to provide alternative housing for people it evicts, as it is required to do by law.

Mr. Tshwaku said the city was trying to speak to tenants of dilapidated buildings individually to determine their needs. When residents can afford a place on their own, city officials work to help them find somewhere to go, he said, and that has helped reduce the number of people who have had to be placed into shelters or other housing.

She spotted her brother’s neighbor, who had burns on her face and was shaken and crying. In the chaos, the neighbor had not seen Mr. Dube.

Ms. Jack’s daughter went to hospitals in the city to look for him. In the meantime, Ms. Jack, 60, kept her gaze on the window of his fourth-floor room, hopeful that the dishes still stacked by the window were a sign that his home had been spared the worst of the fire.

Her brother, in his late 40s, studied law but could never find a job. He set up a workshop in the building’s courtyard, fixing cars to make money. He lived in the building for more than a year, paying 400 rand, about $20, per month for his room.

“I’m just praying he jumped from the window and didn’t die,” she said.

His ascent capped the latest chapter in a political soap opera in which mayoral terms are measured in weeks and months and the inability of council members to stick with a leader has resulted in a municipal mess. Johannesburg residents have been the biggest losers.

While political leaders bicker over power and cliques, exasperated residents often struggle through days without electricity and water, dodge cratered roads and fret about dilapidated buildings, such as the one that caught fire on Thursday.

On Thursday morning, Mr. Gwamanda was at the scene of the fire along with members of the city’s coalition government. He blamed years of neglect for the conditions that led to the blaze, although he vowed that his administration would be accountable.

“This government is only six months old, and already we are facing historic challenges,” he said.

Residents of an apartment complex across the street described the building, which was once an apartheid government checkpoint for Black workers, as a nightmare. It had become a huge squatter camp in a city in the grip of a housing crisis.

People in the neighboring complex said they heard screams at night and sounds that they thought could be gunfire or fireworks. Cars had been stolen from their side of the street, only to be found hidden on the other side of the building where the fire broke out on Thursday.

Pickpockets and thieves would target visitors and disappear into the squalid building, impossible to find, the neighbors said. Drug dealers hung around outside. In the courtyard, corrugated iron shacks had sprung up. Last year, a woman was thrown from the fourth floor of the building, several residents said.

When The Times visited, trash sagged out of second-floor windows. Another pile of trash, at least three feet high, partially blocked the entrance. A street vendor, balancing a crate of oranges on her head, skirted by the trash heap as she entered the building.