Emergency response teams, including police officers, medics and good Samaritans, rushed to the scene shortly after the crash to rescue survivors and recover the bodies of the deceased.
The injured were taken to hospitals in Naivasha and Nakuru for urgent medical attention.
Witnesses at the scene described a horrifying incident, saying the matatu appeared to be travelling at high speed before it crashed into the stationary trailer.
The impact left the vehicle badly damaged, trapping some passengers inside and complicating rescue efforts.
Police have since launched investigations into the cause of the accident.
Preliminary reports indicate that poor visibility and possible driver error may have contributed to the crash, although authorities have not ruled out other factors.
Officers are also working to establish whether proper warning signs had been placed to alert motorists about the stalled trailer.
The Nairobi–Nakuru Highway is one of the country’s busiest transport corridors, linking the capital to the Rift Valley and western Kenya.
The route is frequently used by public service vehicles, private motorists and heavy commercial trucks, making it prone to accidents, particularly in areas with sharp bends or limited visibility.
Road safety experts have repeatedly raised concerns over stalled vehicles being left on highways without adequate signage, warning that such situations pose a serious risk to other road users.
Motorists have also been urged to observe speed limits and remain alert, especially when driving at night or in areas known for frequent breakdowns.
The latest accident has once again highlighted the need for stricter enforcement of traffic regulations and improved response mechanisms for broken-down vehicles.
Authorities continue to urge drivers to exercise caution and adhere to road safety guidelines to help reduce the number of fatalities on Kenyan roads.