The government has vowed to find those responsible and has accused India's intelligence agency of being involved.
This is where officials say a bomber detonated his explosives near a police vehicle as people gathered to mark the birthday of the Prophet Mohammad.
At a local hospital in Mastung, people visited their injured relatives. Many remain in critical condition.
Ghulam Farooq Shahwan is a municipality councillor in a village about 15 miles from the blast.
He says four of his relatives were killed and appealed to the government for help.
"The government should constitute a high-level commission to thoroughly investigate this huge blast," he says.
A second attack on Friday at a mosque in a neighboring province killed at least 5 people.
There's been a surge in militant attacks in Pakistan's western provinces in the run-up to elections in January.
But up until now they had mostly targeted security forces.
No group has claimed responsibility for either attack.
Pakistan's interior minister on Saturday accused India's intelligence agency of being involved.
He did not provide details or evidence on the alleged involvement.
Pakistani officials have long claimed that India sponsors violent groups in Pakistan.
Claims India has always denied.
The Pakistani Taliban (TTP) also denied responsibility for Friday's blasts.
