The bomb was planted on a motorbike parked along the road in Almo Chowk of Quetta city and it exploded when people were busy in shopping during the holy month of Ramadan.
Deputy Inspector General (DIG) of Police Quetta Chaudhary Manzoor said the blast was caused by explosives weighing around six to eight kilograms.
Three people were killed and 32 injured in the attack," a police official said.
"The injured include five children and a woman who are being treated at the Civil hospital while three persons were killed in the blast," he said.
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Security officials rushed to the spot and have started investigations, he said.
Nobody has claimed responsibility for the attack but Taliban and Baloch nationalist militants are active in the area
Eye-witnesses said the blast damaged dozens of shops and nearby homes in the area.
The purpose of the blast appeared was to spread panic and fear in Quetta, the capital city of the Balochistan province, a police official said.
Yesterday, the US had advised its citizens to avoid travelling to Quetta due to a heightened threat in the near term affecting government and military installations, hotels, and western interests in and around the city.