14 people died on the spot while five others succumbed to injuries while undergoing treatment at the Molo District Hospital.
Witnesses say the matatu was overloaded when the breaks malfunctioned before it plunged into the Moto Quarry.
Eight people were seriously injured in the accident that occurred at about 1.00pm.
It comes in the wake of yet another accident where six people were killed after a 14-seater matatu hit a lorry at Subuiga area along Meru- Nanyuki road.
The matatu was heading to Meru from Nanyuki during the 8pm accident.
Several other injured people were rushed to various hospitals in Meru and witnesses blame the matatu driver for speeding.
The accident comes barely hours after 14 other people were killed in separate accidents on New Year.
Eleven of them perished at Salgaa on the Nakuru-Eldoret highway when a matatu they were travelling in collided head-on with a bus, while three others died in separate incidents in Mombasa.