The billiard hall in Quetta, the capital of Baluchistan province, was hit by twin blasts about 5 minutes apart on Thursday night, killing 81 people and wounding more than 120 others, said senior police officer Zubair Mehmood.
The billiard hall was located in an area dominated by Shiite Muslims, and most of the dead and wounded were from the minority sect, said another police officer, Mohammed Murtaza. Many of the people who rushed to the scene after the first blast and were hit by the second bomb, which caused the roof of the building to collapse, he said.
Police officers, journalists and rescue workers who responded to the initial explosion were also among the dead, police said.
The sectarian militant group Lashkar-e-Jhangvi claimed responsibility for the attack to local journalists. One of the group's spokesmen, Bakar Saddiq, said the first blast was carried out by a suicide bomber and the second was a bomb planted in a car and detonated by remote control.
Radical Sunnis groups often target Pakistan's Shiite minority, whom they believe hold heretical views and are not true Muslims.
Earlier in the day, a bomb targeting paramilitary soldiers in a commercial area in Quetta killed 12 people and wounded more than 40 others, said Shakeel, the senior police officer.
The United Baluch Army, a separatist group, claimed responsibility for the attack on the soldiers in calls to local journalists.
Elsewhere in Pakistan, a bomb in a crowded Sunni mosque in the northwest city of Mingora killed 22 people and wounded more than 70, said senior police officer Akhtar Hayyat.
No group claimed responsibility for the attack.
Associated Press writer Rasool Dawar contributed to this report from Peshawar, Pakistan.