The blast at the remote Shah Noorani shrine in Balochistan province, 62 miles north of the port city of Karachi, reportedly took place while hundreds of people were inside.
“Every day, around sunset, there is a dhamaal (ritual dance) here, and there are large numbers of people who come for this,” Nawaz Ali, the shrine’s custodian, told Reuters.
Dozens of wounded people were being moved to the nearby town of Hub and to Karachi, rescue official Hakeem Nasi told Pakistani TV channel Geo TV.
According to local media, there is no hospital nearby and its remote location makes emergency access difficult.
“At least 25 people have been killed in bomb blast at Shah Noorani shrine,” Commissioner of Kalat region Mohammad Hashim told AFP.
Islamic State has claimed responsibility for the attack.