They arrived in desperation, unable to find anything better, safer or cheaper in a city with a severe shortage of affordable housing. They settled in a trash-choked building owned and neglected by the city of Johannesburg, paying “rent” to criminals.

Hundreds of people lived there, and on Thursday morning, at least 74 died there, including at least 12 children, in one of the worst residential fires in South Africa’s history. Flames devoured a structure that overcrowding, security gates, mounds of garbage and flimsy subdividing had turned into a death trap. Some victims leaped from upper windows of the five-story building rather than burn to death.

The disaster came as no surprise to residents, housing advocates or officials of a city that has more than 600 derelict, illegally occupied structures — all but about 30 of them privately owned — according to Mgcini Tshwaku, a city councilman who oversees public safety.

The buildings are home to untold thousands of South Africans suffering from a shortage of housing and jobs, and to migrants from other countries who come searching for opportunity, only to find a nation enduring its own economic crisis. And these urban squatter camps are routinely “hijacked,” residents say, by organized groups demanding payment.

Distraught people milled through the crowd gathered around the building in the downtown area, and went from hospital to hospital, searching for loved ones or anyone who might have scraps of information. Officials said at least 61 survivors were treated at several hospitals.

Looking for her missing brother, Kenneth Sihle Dube, Ethel Jack gazed up at his fourth-floor window, hoping that the dishes she could see still stacked there meant that his corner of the building had not been devastated. She saw bodies covered in foil blankets lined up in the street and spotted her brother’s neighbor, her face burned, shaken and crying.

“I’m just praying he jumped from the window and didn’t die,” Ms. Jack said. He turned up, alive, at a hospital east of the city.

Many of the dead were burned beyond recognition and would have to be identified through genetic testing, officials said. Nomantu Nkomo-Ralehoko, a local health official, told reporters that of those identified so far, two were from Malawi, two from Tanzania and at least two more from South Africa.

People who knew the building said that after the fire began, shortly after 1 a.m., people could have been trapped in the darkness by security gates that were on each floor — though it is not clear which ones were locked — as well as the warren of subdivided dwellings within. Mr. Tshwaku said that bodies were piled just inside a locked gate on the ground floor that had prevented at least some of the victims from escaping.

The authorities said they did not yet know what caused the blaze, which appeared to have started on the ground floor of a building they said housed some 200 families. But in such buildings, where there is no formal electric service, people routinely rely on small fires for cooking, heat and light, and sometimes on dangerous amateur electrical hookups.

“I am surprised more fires haven’t happened,” said Mary Gillett-de Klerk, a coordinator at the Johannesburg Homelessness Network, calling the fatal blaze “an event waiting to happen.”

Visiting the scene, President Cyril Ramaphosa called the disaster “a wake-up call for us to begin to address the situation of housing in the inner city.”

“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.”

But the underlying problems have to do with political dysfunction and economics. Official corruption is endemic, and in the nation that the World Bank ranks as the most unequal in the world, many of the wealthy live in gated communities with private security, while millions of the poor live in ramshackle slums. Three decades after the end of apartheid, inequality still falls largely along racial lines.

Johannesburg’s chronically unstable municipal government has had six mayors in a little over two years, and has failed to address a housing crisis that, like other problems, some politicians have blamed on migrants. Different administrations and political parties accuse each other of graft and of causing political chaos and lack of public services. A fire department that is chronically short of resources dispatched just two engines to the fire on Thursday.

The sprawling building that burned on Thursday once housed offices of the apartheid government, a checkpoint for controlling the movement of Black workers in and out of the city. Mayor Kabelo Gwamanda, who took office in May, said that in recent years the city had leased it to a nonprofit organization that provided emergency shelter for women and children. It also housed a medical clinic.

The city last did a safety inspection there in June 2019, around the time the nonprofit moved out. Inspectors did not return because “we wouldn’t want to go into a hostile environment,” Rapulane Monageng, acting chief of emergency management services for the city, said at a news conference.

Afikile Madiya was living in the women’s shelter when the nonprofit left, and dozens of men started moving in, occupying empty offices on the top floor. They demanded fees from the women and starting moving many more people in, she said, cramming up to 10 people into a room and subdividing it with cardboard, corrugated metal or sometimes just a sheet. She soon moved out.

In October 2019, the authorities raided the building and arrested 140 people in an illegal rent scheme, said Floyd Brink, the city manager, but the case was closed in 2022 for lack of evidence.

New York Times journalists visited the now-gutted building in May while reporting for an article about the chaotic state of Johannesburg. They saw trash spilling out of second-floor windows, a heap of rubbish partially blocking the entrance and a courtyard crammed with corrugated metal shacks housing more people.

Neighbors described the building as a nightmarish shantytown frequented by drug dealers, where a woman was thrown last year from the fourth floor. They said pickpockets and thieves would disappear into the squalid building, impossible to find, while at night screams and what sounded like gunshots emanated from it.

After the end of apartheid, many Black people migrated from rural areas and townships to the city center, where they had been prohibited from living, creating a housing crunch. But since then, advocates say, the government has prioritized the building of private rental units that are priced beyond the reach of most South Africans and of student accommodations, while low-income residents fill long waiting lists for places in public housing.

“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 most affected by the housing crisis.

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

Beginning in the 1990s, many landlords, fearful of the direction of the new South Africa, abandoned downtown buildings and let them fall into disrepair, said Khululiwe Bhengu, a senior attorney with the Socio-Economic Rights Institute of South Africa, a nonprofit. The buildings slowly filled up with squatters, and officials say that criminal syndicates moved in, demanding payment from the new residents.

“People are occupying these buildings because there’s nowhere else where they can access the inner city,” Ms. Bhengu said.

Mr. Tshwaku, the city councilman, said he had started a program this year to inspect such buildings and get people to move out of them. So far, 14 of the more than 600 buildings have been inspected, he said, but it is not clear how many people have relocated.

That effort is hampered by the fact that, legally, officials cannot remove people from their dwellings, even those who are present illegally, without providing alternative housing, if the residents show that they cannot find new accommodations on their own.