The 52-seater bus was ferrying passengers for Christmas and New Year festivities.
Among those killed included a police officer in the grisly accident that occurred at the Kericho junction to Kisumu.
The injured were rushed to the Kericho District Hospital.
The 52-seater bus that plies the Thika Road route, from Githurai 45 to Nairobi Central Business District, was ferrying passengers to Kisumu for Christmas and New Year festivities.
According to the Kericho County Commander James Mugera, the brakes of the bus failed before the driver lost control.
"The bus' brakes failed as it went down the slope from town. As it approached Kisumu road, where traffic police conduct checks, a lorry was negotiating the spikes. The bus then hit the lorry before landing in a swampy ditch," Mugera told The Nation.
The bus which lost control later hit and killed a Traffic police officer on the spot at the roadblock.