At least 14 people ─ including seven policeman ─ lost their lives, while 19 others were injured in a suicide blast that shook Shuhada Chowk in Quetta's Gulistan Road area on Friday morning, police said.
The injured were moved to Quetta's Civil Hospital, where an emergency was declared. Security was tightened across the city following the attack.
According to DawnNews, the blast occurred close to Inspector General of Police Ehsan Mehboob's office.
The blast was powerful enough that it was heard across the city, shattering windows of nearby buildings, said police spokesman Shahzada Farhat.
TV footage showed several badly damaged cars and a road littered with broken glass.
Director General of Civil Defence Mohammad Aslam Tareen said 75 kilogrammes of explosives were used in the suicide attack.
Deputy Inspector General of Police Abdul Razzaq Cheema, while talking to media, said it had not been determined yet who was being targeted in the attack.
"This road sees a lot of traffic and movement; however the timing of the blast did not coincide with rush-hour traffic, so we are not sure of what was targetted," the DIG said.
Security forces had reached the area soon after the bombing, cordoned it off and launched an initial investigation, DawnNews reported.
Anwarul Haq Kakar, a spokesman for the provincial government, said the bomb was planted in a moving car.
No one claimed responsibility for the attack, but Kakar blamed India for the blast. He offered no evidence.
On Thursday, Pakistan said that Indian naval officer Kulbhushan Jadhav, who was sentenced to death by a Pakistani military court on charges of espionage and sabotage, had petitioned for mercy.
In a 'confessional' video released simultaneously with the announcement of Jadhav's appeal, the spy was heard saying that Indian intelligence agency Research and Analysis Wing (RAW) sponsored various terrorist activities in Pakistan in order to disrupt economic activities linked to the China-Pakistan Economic Corridor.
Jadhav, who Pakistan said had crossed into Balochistan from neighbouring Iran, was arrested in March 2016 and sentenced to death in April.
Balochistan has faced a number of security challenges in recent months, with security personnel in the province often being targeted in roadside explosions.
Earlier this month, three security officials were injured after an improvised explosive device (IED) seemingly targeted their vehicle in the Johan area of Kalat.
Days later, two navy sailors were martyred and at least three others were wounded when their vehicle was attacked in the Jiwani area of Gwadar district.
In May, at least 10 labourers were killed in Balochistan's Gwadar district when unidentified assailants opened fire at the construction site where they were working.