Videos spreading online showed a dramatic crash and huge clouds of dust as the building came down in the densely populated business and residential area.
A 12-storey building under construction in Kenya's capital Nairobi collapsed on Friday, with the Nairobi County governor's office saying there were reports people may be trapped beneath the rubble.
It was not immediately clear what caused the building to collapse.
Governor Johnson Sakaja's office said the ground floor of the collapsed building in the Eastleigh neighbourhood was occupied.
A Reuters video showed a crowd had gathered at the scene while an excavator moved rubble.
Videos spreading online showed a dramatic crash and huge clouds of dust as the building came down in the densely populated business and residential area.
AFP journalists at the scene saw the building had been reduced to a pile of rubble as search and rescue teams arrived on the scene.
AFP saw police use tear gas to disperse crowds gathering near the site.
Nairobi is undergoing a rapid construction boom, with high-rise buildings appearing all over the city, particularly in Eastleigh which is known for its busy market areas .
There have been many concerns over safety.
The number of buildings completed annually in Nairobi has risen from 20,025 in 2022 to 25,090 last year, according to its statistics bureau.
