The bomb went off near the village of Mach in the Baluchistan province, a railways official Tufail Ahmad told The Associated Press.
He said the train was heading to the garrison city of Rawalpindi in the eastern Punjab province from Quetta, the provincial capital of Baluchistan at the time. Ahmad said the casualties were taken to nearby hospitals and that some of the wounded passengers were in critical condition.
Initially three people were reported dead but three more later died of their injuries, said Mohammad Sajid, local police chief.
No one immediately claimed responsibility for the attack, but separatist groups in the province have claimed similar attacks in the past. Baluchistan has long been the center of a low-level insurgency by nationalist groups that demand more autonomy and a greater share in the region’s natural resources.
The government says it’s trying to improve people’s welfare in the province and bring the separatists into mainstream politics.
Railways Minister Khawaja Saad Rafique denounced the bombing as “an act of terrorism” and said authorties were still trying to determine how the bomb was planted on the train.
Prime Minister Nawaz Sharif condemned the attack and ordered authorities to find and arrest those behind it. In a statement, he also ordered health official to provide best medical care to the wounded passengers.