Three middle-aged men died in Ruiru, Kiambu County, while unloading granite from a container trailer that had ferried the material from Industrial Area in Nairobi.
While eight people had begun to offload the stones packed on the left and the right, the construction materials fell on top of them.
Four, according to Ruiru Sub-County police commander Alex Shikondi, managed to jump out of the vehicle while another suffered serious injuries and is recuperating in hospital.
Three others, according to Shikondi, died after the granites accidentally fell on top of them, leaving them dead.
Survivors recounted the horrific incident, saying they tried to rescue them.
Locals said the deceased were not experts in unloading materials such as granite, adding that the container was slightly tilted to one side, making it harder to unload granites.