The blast occurred at Kirani Road in Hazara Town, a suburb of Quetta with a large Shia population that has been targeted by terrorists in the past.
The bomb was hidden in a vehicle and triggered by remote control, DIG Wazir Khan Nasir told reporters. He said the Shia Hazara community was the target of the attack.
Officials at the Bolan Medical Complex, Civil Hospital and a military hospital said 63 people had died and about 200 injured were being treated. Several women and children were among the dead. The death toll could rise as some of the wounded were in a serious condition, officials said.
Officials said the vehicle with the bomb was parked near the pillar of a building in a market. The building collapsed due to the intensity of blast and several persons were trapped in the debris. An estimated 100 kg of explosives was used in the attack, officials said.
Footage on television showed several buildings were reduced to piles of rubble by the blast that was heard all over Quetta, the capital of the restive Balochistan province. Several shops and vehicles were destroyed. Angry people took to the streets and protested against the attack.
The protesters pelted vehicles with stones and prevented rescue workers and police from approaching the site of the blast for some time. They also blocked roads and fired in the air.
Security forces cordoned off the area and did not allow the media to approach the site of the blast.
Officials said this was done as terrorists had set off a bigger bomb after a smaller initial blast in recent attacks.
No group claimed responsibility for the blast. Similar attacks in the past have been blamed on the banned Lashkar-e-Jhangvi.
President Asif Ali Zardari and Prime Minister Raja Pervez Ashraf condemned the attack on Saturday.