Three people died on Saturday afternoon after a matatu they were travelling in was involved in an accident with three other vehicles at Sachang'wan on the Nakuru-Eldoret highway.
Thirteen other people were seriously injured when a truck from Eldoret rammed into St Patrick's Iten Secondary School bus and two matatus all travelling in the same direction.
Nakuru county traffic commander Mary Omari said the truck's brakes are suspected to have failed, causing it to ram into other vehicles ahead of it.
The impact then caused a matatu belonging to Eldoret Cross Road Sacco to veer off the road and crash, killing three of its passengers instantly.
No one in the school bus that was headed to Mombasa for the schools music festival was injured.
Majority of the injured, who were travelling in the two matatus, were rushed to the Molo District Hospital.
Witnesses said the truck driver might have been unaware of new speed bumps recently erected on that section of the road and had been speeding when the accident occurred.
In a separate accident in Naivasha on Sunday, three passengers including the driver of a matatu were seriously injured and rushed to Naivasha sub-county in critical condition.
The Nissan matatu belonging to Molo Group veered from its lane and rammed in an incoming lorry near Marura farm in Naivasha along the Nairobi-Nakuru highway.