The bomb was detonated by remote control outside a commercial building in Mastung town. The market was crowded with people shopping ahead of the Eid-ul-Fitr festival.
A 35-year-old woman, an eight-year-old boy and a 12-year-old girl were among the dead, police said. Several women and children were wounded.
Officials said the number of casualties would have been higher if the bomb had been planted inside the building.
"The bomb was planted near the shopping centre and targeted Eid shoppers. The victims were taken to nearby hospitals," a police official said.
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Yesterday, militants disguised as security personnel stopped two buses going to Punjab province from Quetta, the capital of Balochistan, and gunned down 13 men.
The men, mostly of Punjabi origin and labourers, were pulled off the buses and taken to nearby mountains, where they were shot.
One security personnel was also killed in the brazen attack in Bolan district.