The attackers opened fire on a police van patrolling at the Munir Mengal Road area killing two policemen on the spot, while two others sustained serious injuries in the drive-by shooting incident.
The gunmen fled from the scene on their motorbikes after the attack, police officials said.
Injured policemen were rushed to Civil Hospital in a precarious condition for medical treatment.
The law enforcement agencies personnel reached to the spot and and initiated investigation of the incident.
Attacks on police
Quetta has witnessed scores of attacks on policemen including a suicide attack at outside a polio vaccination centre earlier in this month, which left 15 people dead including 12 policemen.
Policemen were earlier attacked in Satellite Town, Sariab Road and Pashtoonabad areas of Quetta, the capital city of southwestern Balochistan province of Pakistan.