Three teachers and one student from Starshine Blue school, Kiambu sustained serious injuries after the bus they were travelling in veered off the road landing on its side.
The accident happened along the Nairobi-Nakuru highway at Raini trading centre, around 50 kilometers from Naivasha town, on Thursday morning.
Trouble started after the bus destined for Nakuru National Park developed mechanical problems, the driver claiming break failure, thus forcing the bus to veer off the road.
According to one witness James Njoroge, the bus was on high speed when the accident occured.
He further said that the bus hit some speed bumps along the road, lost control and started swaying from one side of the road to the other.
"It is by goodluck that there were no other vehicles on the road at that time as the bus swerved from one side to the other before crashing on one of its side," said Njoroge.
Another witness denied claims that the bus developed mechanical problems, citing that the speed bumps erected there caused the accident.
"Just like other accidents, the driver spotted the speed bumps when it was too late and this led to the accident,"he said.
20 other students sustained minor injuries and were treated at Naivasha sub-county hospital and discharged.