In the first incident, three persons were killed and around nine injured when militants lobbed grenades at two barber shops on the Double Road area of the city.
"It appears the attackers came on motorcycles and threw two hand grenades at these two shops which were packed with customers," a senior police official said.
"The attackers appeared to target the settlers who owned the barber shops," Muhammad Aslam said.
The shop owners were believed to be from the Punjab province.
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The injured persons were rushed to Civil Hospital Quetta for medical treatment where an emergency was imposed.
The blast also damaged some vehicles and smashed the glasses of nearby homes and shops.
An hour later, attackers again threw a hand grenade at a photographer's shop on Saryab road in which one person was killed and two others injured.
Police said the shop was damaged during the blast that rocked the entire Sariab road area of Quetta.
Earlier on September 21, at least 11 people, including a woman, were injured when a powerful explosion that took place in the Jinnah Town neighbourhood of Quetta.