Officials said 55 more were injured in the blaze in Johannesburg, which broke out in the middle of the night.

Robert Mulaudzi, a spokesman for the emergency services, has warned the number of fatalities may rise further - as more people could be trapped inside.

There were "obstructions" everywhere, and this would have made it difficult to escape.

Firefighters have been currently going from floor to floor - working slowly through the building's five storeys.

"Over 20 years in the service, I've never come across something like this," Mr Mulaudzi added.

Witnesses saw people throwing babies from the burning building in an attempt to save them - and at least one man jumped to his death.

Seven of the victims were children - and the youngest was a year old.

One woman who escaped the flames with her grown son and a two-year-old said she didn't know what had happened to two other children in her family.

The building in the central business district has been described as an "informal settlement" where homeless people had moved in looking for accommodation. Some of the victims may have been renting rooms from criminal gangs.

According to witnesses, at least 200 people may have been living there - maybe more - and many of them were foreign nationals.

People looking for their loved ones have been warned that chances of finding them alive are "very slim".

One woman looking for her daughter tearfully told reporters: "This is not a place where somebody can live. I was trying to get her to come back home so she could get back to the life she was living before."

Firefighters evacuated occupants after arriving at the scene - but now, a search and recovery operation is under way. Bodies lay covered on the street.

Authorities said the fire is largely extinguished, but smoke still seeped out of windows of the blackened building. It took three hours to contain.

Abandoned and rundown buildings are common in the area, and are often used by people desperately seeking accommodation.

They are referred to as "hijacked buildings" - and the government says this tragedy demonstrates a "chronic problem" as at least 1.2 million people need housing in the province.

A sign at the entrance shows it was a heritage building linked to the country's apartheid past, where black South Africans would collect documents allowing them to work in white-owned areas.

During a news conference, one reporter asked officials whether more should have been done to help the building's residents before the fire - but he was told the question was "dramatic" and "insensitive".

Strings of sheets and other material hung out of broken windows - makeshift ropes that those inside tried to use to escape.

One person who lives in a nearby building heard people screaming for help and shouting "we're dying in here".

The cause is yet to be established - but there are indications that people lit fires inside the building to keep warm. Initial evidence suggests the fire was started by a candle.

This is one of South Africa's worst tragedies of its type in living memory.

Johannesburg is one of the world's most unequal cities - and suffers from widespread poverty and joblessness.

Fires are common, and it suffers from chronic power shortages.