The accident involved a Garissa-bound bus which lost control and rolled several times at about 3am, according to Traffic Commandant Samuel Kimaru.
Eleven people were killed on the spot while the rest were trapped under the wreckage and it took rescuers more than four hours to help them out.
“It was a very bad accident, it took a lot of time for them to be rescued because the bus was badly damaged,” he said.
Kimaru said more than 20 other passengers have been admitted to the Mwingi District Hospital.
The Traffic Commandant said they have not established the exact cause of the accident that occurred at Tulimani area.
“We don’t know what exactly happened but we are urging motorists to be careful to avoid such accidents. We could not have lost the 35 people, if drivers were careful on the road,” added Kimaru.
Over the weekend, at least 17 people were killed and scores injured in two separate road accidents in Voi and Kilifi on Saturday morning.
In the first accident that happened at Ndii near Voi, 12 people died on the spot after a bus and trailer collided. The dead included 10 men and two women as well as drivers of both vehicles.
Fourteen other people were injured and were rushed to the Voi District hospital for treatment.
Police said that the bus which was heading to Mombasa from Nairobi was overtaking another vehicle before it collided with the oncoming trailer.
“This is purely a case of human error, the bus driver was trying to overtake when there is a trailer approaching,” Kimaru told Capital FM News following the 4am accident last Saturday.
The second accident in Vipingo area in Kilifi that claimed five lives involved a matatu and a private van that had previously operated as tour van.