The bomb containing nearly a ton of explosives, hidden in a water tanker, tore through a crowded market in Hazara town, a Shiite-dominated area on the edge of Quetta, the capital of southwestern Baluchistan province, on Saturday evening.
Mourners gathered on Sunday as people sifted through the rubble of the explosion, many weeping as they discovered limbs and pieces of flesh torn apart by the blast, which wounded 178 people.
Witness Zainab Bibi, 38, said the carnage was "like the day of judgment had come".
"Initially I could not see anything because of a thick cloud of dust but I could hear loud screaming," she told AFP.
"As the dust settled, I saw blood everywhere, torn bodies were lying everywhere with no clothes on."
The governor of Baluchistan blamed failures by intelligence and security agencies for the attack, saying they were too frightened to deal with groups behind sectarian violence.
Baluchistan has increasingly become a flashpoint for surging sectarian violence between Pakistan's majority Sunni Muslims and Shiites, who account for around a fifth of the country's 180 million people.
Saturday's attack takes the death toll in sectarian attacks in Pakistan this year to almost 200, compared with more than 400 in the whole of 2012 -- a year which Human Rights Watch described as the deadliest on record for the country's Shiites.
It was the second major attack on Shiites in Quetta this year, after a double suicide bombing on a snooker club in the city on January 10 killed at least 92 people, the deadliest ever attack on the community in Pakistan.
More than 1,500 Shiites took to the streets of the eastern city of Lahore to demand action against the extremists, and there were smaller demonstrations in the central city of Multan and Muzaffarabad, the main city of Pakistan-administered Kashmir.
The banned militant group Lashkar-e-Jhangvi (LeJ) claimed responsibility for Saturday's attack -- as it did for the snooker hall bombing and a February 1 attack on a Shiite mosque in northwest Pakistan that killed 24.
There is anger and frustration among Shiites at the apparent inability or unwillingness of the authorities to tackle the LeJ. Activists say the failure of the judiciary to prosecute sectarian killers allows them to operate with impunity.
Baluchistan governor Zulfiqar Magsi pointed the finger at the security forces over the latest atrocity.
"Repeated occurrence of such attacks is a failure of our intelligence agencies," he told reporters late on Saturday.
"Our security institutions, police, FC (paramilitary Frontier Corps) and others are either scared or cannot take action against them."
Sayed Qamar Haider Zaidi, a spokesman for Shiite groups in the area, condemned the Pakistani government for not providing protection to the community and announced three days of mourning and protest over the attack.
Pakistan's national flag was flying at half mast after the provincial government declared a day of mourning over the killings and markets were closed.