Levies officials said the bus was going from Noshki to Kharan when it overturned in Noshki district.
"Those killed and injured included women and children," officer Muhammad Anjum said.
"The bus overturned because it was overspeeding and the driver apparently lost control of the vehicle," he added.
Two passengers were killed on the spot and four others succumbed to injuries on their way to the hospital.
Anjum said more than two dozen passengers were shifted to district hospital in Noshki for medical treatment.