The bomb went off as a truck carrying 35 police personnel was passing the area.
The nature of the blast has yet to be ascertained.
Balochistan Home Minister Sarfaraz Bugti while condemning the attack confirmed that six policemen had lost their lives in the attack while 22 others were injured and being treated at the Civil Hospital and Combined Military Hospital (CMH) in Quetta.
Police and FC troops have reached the area, which has been cordoned off for gathering evidence.
The Tehreek-i-Taliban Pakistan claimed responsibility for the attack. According to hospital staff, the condition of seven injured was critical.
"We can not yet say that this is a suicide attack, our teams are in research and investigations at scene", Cheema said.
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Balochistan Chief Minister Nawab Sanaullah Khan Zehri strongly condemned the attack, adding that such attack could not discourage the security officials from fighting the terrorism.
"Such cowardly acts will not deter the government and people of Balochistan from doing their duties", Bugti said, adding the fight will continue till the elimination of the last terrorist.
In the drive-by shooting, two men on a motorcycle shot and killed police inspector Abdus Salam as he was on his way to work.
Baloshistan has witnessed several blasts and targeted killings in the past few months.
"A forensic team is reaching from Lahore and will determine whether it was a suicide bomb attack or whether explosives were detonated close to the vehicle", Bugti said. PM Abbasi expressed deep grief and sorrow over the loss of precious lives during the terrorist attack.
The attack took place on Sibi Road in Sariab area.