The accident that involved a bus ferrying passengers and a trailer occurred at 3am, according to police.
Makindu OCPD Sarah Duncan said the Mombasa-bound bus rolled at Makindu while overtaking the trailer.
“The Crown (bus company) tried to overtake trailer at makindu bridge and the driver realized too late of an oncoming vehicle and in the confusion he hit the trailer,” she said.
Three people died on the spot and four others were declared dead on arrival in hospital.
“Those who died on the spot include a man, a woman and a girl,” Duncan said.
Ten people were seriously injured and 30 others escaped with minor injuries.
Most of the injured were rushed to Makindu District Hospital and Machakos District Hospital.
Road accidents have been on the increase in the last one month and police blame drivers who often flout the highway code.