The injured, three of them critically, were admitted to the Embu Level 5 Hospital.
“Of those admitted, nine are male including a boy below 10 years while three are female,” the hospital Medical Superintendent Gerald Ndiritu said.
According Martin Murithi, who witnessed the accident, the matatu which was travelling towards Embu town was overtaking a motorcyclist downhill when it collided with the lorry.
The area where the accident occurred is a known black spot.
Among the dead was the driver of the lorry who was travelling alone.
Murithi said many of the residents who arrived at the scene started stealing from the victims instead of rescuing them.
Kennedy Murimi, 17, who was among the survivors said: “The driver appeared to lose control of the vehicle and it started swaying. The driver accelerated while overtaking the motorcycle,” he said.
Another survivor, Lewis Fundi, who suffered several bruises said the vehicle started wobbling while going down the hill.
“After the accident, I was retrieved from under the lorry,” he told the media at the hospital where he was receiving treatment.
Traffic police and Red Cross officials arrived at the scene and helped evacuate the injured and retrieve the bodies.
The bodies were taken to the Embu Level 5 Hospital mortuary.