JOHANNESBURG: More than 70 people were killed overnight when fire raged through a five-storey apartment block in a poor area of Johannesburg, officials said on Thursday, adding that some of the victims may have been renting rooms there from criminal gangs.

At noon, the munipical-owned building was still smouldering, a large part of it blackened by soot, as emergency services gathered around it and bodies lay covered in blankets on a nearby street, a Reuters reporter said.

Leo, a 25-year-old who survived the blaze, had been living on the second floor. He escaped along with his mother via the stairs.

"People were just running away. It was dark and there was smoke. You couldn't see anything," he said.

At least one person jumped to their death, said Thando le Nkosi Manzini, a student who saw the blaze from the street. "I saw a guy jumping from the fourth floor," he told Reuters.

The blaze, which started at around 1.30 a.m., killed at least 73 people and injured 43, the municipal government said, in one of South Africa's worst such tragedies in living memory.

Johannesburg authorities initially suggested the building had been occupied by squatters.

But city Mayor Kabelo Gwamanda told reporters it was owned by the municipal authorities and had been leased to charity for displaced women but had "ended up serving a different purpose," without giving further details.

Lebogang Isaac Maile, the head of the Human Settlements department for Gauteng province, which includes Johannesburg, later said some of the victims may have been renting from criminal gangs illegally collecting fees.

"There are cartels who prey on who are vulnerable people. Because some of these buildings, if not most of them, are actually in the hands of those cartels who collect rental from the people," he told reporters at the scene.

APARTHEID HERITAGE BUILDING

A sign on the entrance to the gutted block showed it was a heritage building to South Africa's apartheid past, where Black South Africans came to collect their "dompass" - documents that would enable them to work in white-owned areas of the city.

Authorities said the cause of the fire was still under investigation.

Johannesburg is one of the world's most unequal cities with widespread poverty, joblessness and a housing crisis. It has about 15,000 homeless people, according to Gauteng's provincial government.

Fires are common in Johannesburg, especially in poor areas. One of the poorest townships of Alexandra has seen hundreds of homes razed in several fires over the past five years.

The city suffers from chronic power shortages during which many resort to candles for light and wood fires for heat.

Maile said the fire "demonstrates a chronic problem of housing in our province, as we've previously said that there's at least 1.2 million people who need housing."