A bomb disposal team scoured the site for evidence.
The blast occurred as a group of policemen were conducting routine checks in the area.
Reports said a Shia police officer was the target of the attack though this could not immediately be confirmed.
No group claimed responsibility for the attack.
Quetta and other cities across Balochistan have witnessed a series of sectarian attacks targeting the minority Shia community.
Most of the attacks have been blamed on the banned Lashkar-e-Jhangvi.
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