A fire at a five-story building in downtown Johannesburg Thursday morning left at least 63 people dead and more than 40 injured, city officials announced.

The fire in South Africa's largest city broke out around 1:30 a.m. local time, according to the City of Johannesburg Emergency Management Services. When firefighters arrived at the scene, crews immediately began evacuating those inside the building and working to contain the fire.

As of 8 a.m. local time, the flames were mostly extinguished, but smoke was still trickling out of windows. 

Spokesman Robert Mulaudzi said a search and recovery operation was underway within the building and 63 bodies had been pulled out so far. The Associated Press reported at least one child was among the dead.

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There were also 43 people treated at the scene for injuries, Mulaudzi said. The extent of their injuries was not revealed, but he said they were all transported to hospitals in the area for further care.

Relief for families affected by the fire has been activated by City of Johannesburg Disaster Management.

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Mulaudzi said the building had been overtaken by homeless people looking for a place to live without formal lease agreements, which made it difficult to search, according to The AP.

"Over 20 years in the service, I’ve never come across something like this," Mulaudzi told the outlet.

Witnesses told local news outlets there could have been as many as 200 people living in the building.

The cause of the fire remains under investigation.

This is a developing story. Check back for updates.