Suspected militants threw explosives at a shop selling Pakistani flags for Independence day at Prince Road area of the city, Superintendent of Police Imran Qureshi said.
"The bomb exploded with a loud bang, wounding 22 people," Qureshi said, adding that the explosion also damaged the shop and nearby parked vehicles.
The injured were rushed to a hospital for treatment.
The militants fled on their motorcycle after the attack.
Baloch separatists have in the past carried out attacks on government buildings and installations. They have also warned people against celebrating Independence day.
The insurgents had attacked the historical monument with hand grenades, destroying the building where the founder of Pakistan Mohammad Ali Jinnah spent his last days.
