Chaman is located near the country's border with Afghanistan.
The blast, which occurred on Taj Road in Chaman, shattered windows in nearby buildings.
According to police officials, the bomb was an improvised explosive device (IED) which was planted in a motorcycle parked on the roadside.
The explosion has left Maulana Hanif, a central leader of Jamiat Ulema-e-Islam Fazl critically injured. Police say he was the target of the attack.
The injured have been shifted to Civil Hospital Chaman, where an emergency has been declared.
No group has claimed responsibility for the attack so far.
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