According to police, the explosion was planted in a motorcycle parked near Hazar Ganji market.
The blast has also caused damage to nearby shops and parked vehicles, said police.
Meanwhile, rescue workers rushed to the area and shifted the injured to Civil Hospital Quetta.
On getting information, a contingent of security forces also reached the area and cordoned it off to collect evidence.
In a statement, Chief Minister Balochistan Abdul Qudus Bizenjo has condemned the attack and prayed for the early recovery of the injured.
The chief minister also directed authorities concerned to tighten security in the provincial capital.
In a similar type of incident reported from Quetta on Friday, a man was killed and 14 others, including two children, were injured in a grenade attack targeting roadside stalls selling national flags.
The blast took place at the Joint Road Square near Raisani Road.