Gunmen kidnapped 25 passengers from two Karachi-bound buses near Quetta and killed 19 of them late on Friday, in the second such attack on bus passengers in the country this month.
About 15 armed men dressed in uniform of security forces carried out the attack in the town of Mastung near Quetta on Friday.
Security forces who arrived at the scene engaged in gunfire with the terrorists, but could only rescue five passengers who survived the attack.
"Security forces found the bodies of 19 passengers in the mountains," Balochistan Home Minister Mir Sarfaraz Ahmed Bugti told Dawn.
The passengers were mostly traders and labourers from the Pishin district and were travelling to Karachi.
Balochistan is one of the most restive regions in the terror-plagued nation, and civilians often bear the brunt in fighting between insurgents and security forces.
No group has yet claimed responsibility for Friday's attack.
The attack comes days after 43 Ismailis were shot dead in a bus in Karachi, in one of the deadliest attacks on the minority Shia community in Pakistan.
Isis had claimed the attack.