The bus was overloaded and speeding, a survivor told local media. The Western Express bus was from Nairobi and heading to Kakamega.
The extra passengers were seated on the bus floor since all seats were occupied.
However James Mugera, the Kericho County Police Commander, said there were 50 fatalities: "Those who perished include 31 male passengers, 12 women and seven children".
Police said the driver had lost control and plunged down a slope at a notorious accident black spot.
The government agency in charge of road safety said the bus did not have a license to travel at night.
The wrecked bus is seen at the scene of a bus crash near Kericho in western Kenya Wednesday, Oct. 10, 2018.
The injured were taken to the Fort Ternan dispensary and Muhoroni Sub County Hospital for treatment.
President Uhuru Kenyatta, DP William Ruto and opposition chief Raila Odinga have led the nation in mourning the loss of lives after the grisly road accident that occurred at Fort Ternan area on the Kisumu - Muhoroni highway.
"As authorities investigate the cause of the accident with a view of taking action, I would like to remind drivers to always exercise caution to avoid such catastrophic incident", he said on Twitter.
Kenyans on social media, have called out the transport regulators for failing to rein in road accidents, considering that the accident scene is a known black spot that has registered nearly 10 accidents this year.