One of the victims is a police officer who was travelling back home from an interview in Nairobi.
The driver of the lorry fled the scene after the accident.
Four people were killed on Wednesday night after a 14-seater matatu rammed a lorry on the Narok-Maai Mahiu highway.
Narok East Deputy Police Commander M’amburugua Muthamia said the accident occurred at Stima area. Four people were taken to Narok Referral Hospital with serious injuries, the police boss said.