Police told Reuters at the scene the initial report was that the driver lost control of the vehicle and a few survivors had been taken to nearby hospitals.
Residents near where the crash occurred, who ran to the scene, said they had managed to save a few people who were alive but the others were already dead.
Police and rescuers had counted 50 people dead, including seven children. Authorities are investigating the cause of the accident.
The Daily Nation newspaper quoted Traffic Commandant Samwel Kimaru as saying that 2,345 people have died in road crashes across Kenya in the past 10 months, an eight percent rise compared to last year.