JOHANNESBURG, South Africa  -- A fire that ripped through a five-storey building taken over for illegal housing has killed 74 people including 12 children in central Johannesburg, South African authorities said Thursday.

Another 61 people were injured and received hospital treatment in what was one of the deadliest fires worldwide in recent years.

Bodies were discovered piled up at a security gate that was closed, preventing people from escaping the blaze, an official said.

Thembalethu Mpahlaza, the head of forensics services in Johannesburg's Gauteng province, said a total of 74 bodies were recovered, 24 female, 40 male and 10 "burnt beyond recognition".

"We are having 12 children involved also in this tragedy," he said at a press conference.

City authorities said the municipality-owned, listed building in an economically depressed, crime-ridden area had been turned into illegal housing after being abandoned.

Most of those living there were foreigners, one resident said.

"I'm grateful to be alive, there was a lot of us running, trying to find the fire exit and a lot of people eventually died because of the smoke inhalation," said Kenny Bupe, a survivor caught up in the blaze while visiting a friend.

The 28-year-old told AFP he was in a group that managed to break open a locked fire escape gate and run to safety, while others "jumped out" of windows.

Blankets and sheets used for escape hung from the burned-out windows after the flames were put out.

Witnesses spoke of parents throwing their babies out into the street, hoping to save them.

"There were people catching the babies and there were also mattresses laid out for (them)," said Mac Katlego, 25, who lives across the street.

By Thursday evening, rescuers were wrapping up search operations before handing the scene over to police.

- Security gate closed -

"This is a great tragedy, felt by families whose loved ones perished in this terrible manner," South African President Cyril Ramaphosa said at an event in the southern city of Gqeberha.

Visiting the scene later in the evening, he said authorities were working "full out" to assist those affected, adding the disaster needed to be investigated.

"It's a wake-up call for us to begin to address the situation of housing in the inner cities," Ramaphosa said.

It was not immediately clear what caused the blaze. House fires are fairly common in South Africa, plagued by chronic power outages, where poverty and homelessness are widespread.

Authorities said candles used for lighting inside the structure or stoves and other heating devices were a likely cause.

The building, which has been evacuated, is located in what used to be the business district of South Africa's economic hub and was used as an informal settlement by people squatting there illegally, authorities said.

"Inside the building itself there was a (security) gate which was closed so people couldn't get out," said Mgcini Tshwaku, a member of the city's mayoral committee in charge of public safety.

"Many burned bodies were found stashed at that gate."

During the day, firefighters damped down hotspots as emergency services laid dead bodies under blankets on the street outside.

Paramedics assisted survivors, some looking bruised and visibly in pain.

- Bodies on the ground -

"The scene this morning was a mess, there were bodies on the ground everywhere," said Noma Mahlalela, 41, a resident, adding most people living at the premises were foreigners.

Authorities estimated more than "80 shacks" were set up inside.

"The fire spread very quickly, affecting different levels of the building, because of the combustible materials used," said Emergency Management Services spokesman Robert Mulaudzi.

Illegal occupation of disused buildings in Johannesburg's city centre is widespread, with many said to be under the control of criminal syndicates.

The building was raided by police in 2019, when 140 foreign nationals were arrested for illegally collecting rent, Johannesburg city manager Floyd Brink said.

"It was so difficult for us to get out," said Nobuhle Zwane, who managed to escape with her two children aged two and 13, adding that some corridors were blocked by beds.

"We did inhale quite a lot of smoke."

Residents told AFP each of the five floors had a security gate that was kept locked at night to keep out police and possible intruders.

South Africa, with the continent's most industrialised economy, attracts millions of migrants, many undocumented, from other African nations.

Condolences poured in, including from the head of the African Union Commission, Moussa Faki Mahamat, and Ukrainian President Volodymyr Zelensky.

UN Secretary-General Antonio Guterres said he was "deeply saddened" by news of the fire.

UN teams in South Africa are "ready to work with the authorities to provide assistance to those affected and to prevent further incidents of this nature", his spokesperson Stephane Dujarric said in a statement.