The blast hit a crowd of worshippers participating in a ceremony at the shrine of Sufi saint Shah Noorani in Khuzdar district, some 760 kilometres (472 miles) south of provincial capital Quetta.
"At least 25 people were killed and 30 others were wounded in a bomb blast at the shrine of Shah Noorani," local government official Javed Iqbal told AFP.
Hakim Lasi, a rescue official with the Edhi Foundation, Pakistan's largest welfare organisation, told Geo TV channel that the charity had received reports via wireless radio saying that up to 30 people had been killed and nearly 100 others wounded, including women and children.
Local officials said worshippers were taking part in a devotional dance session, which is held daily before dusk, when the blast hit.
The attack comes months after Amjad Sabri, a renowned Sufi singer, was shot dead by two gunmen in Karachi in June.
Some observers have said that Sabri may have been assassinated because he was a high-profile Sufi.
Sufism, a mystic Islamic order that believes in living saints, worships through music, and is viewed as heretical by some hardline groups including the Taliban.
