A local candidate is one of the dead in the city of Mastung, according to police. The so-called Islamic State (ISIS) claims to be the party behind the attack.
Earlier, a bomb attack on a similar campaign in the northern town of Bannu killed four people. The attack came ahead of elections on July 25.
Meanwhile, former Prime Minister Nawaz Sharif was arrested after flying home from Britain.
Sharif and his daughter Maryam were secured by National Accountability Bureau (NAB) officials after landing in the northern city of Lahore. They were then placed on a chartered plane bound for Pakistan’s capital, Islamabad.
They were then transferred to a local prison.
The three – times prime minister was ousted last year after a corruption inquiry. Last week he was sentenced in absentia to 10 years in prison.
He accused the powerful Pakistani security agency of conspiring against him ahead of elections.
Among those killed were the provincial assembly candidate of Baluchistan, Siraj Raisani, his family said. He is a candidate for the Balami Awami party.
Local officials said the attacker detonated a bomb between the crowds where the campaign was held.
“Human body cuts and bloody red flesh are scattered everywhere in the compound,” local journalist Attah Ullah was quoted as saying by the AFP news agency.
“The wounded people are crying in pain and fear,” the reporter said.
ISIS militants then use their news outlets to claim as the group that carried out the attack.
ISIS has carried out a number of attacks in the region bordering Afghanistan in recent years. However, security has improved since the military managed to clear most of the region.
Friday’s bomb was the deadliest attack since Pakistani Taliban militants attacked an army-run school in Peshawar in December 2014, killing 141 people, 132 of them children.
Earlier in the day, another prospective campaign convoy was attacked in Bannu.
Akram Khan Durrani, who represents the MMA party, was not injured, officials said.
No group has claimed responsibility for the attack.
On Tuesday, a suicide bomber raided a campaign in the northern city of Peshawar, killing 22 people – including a provincial candidate.
The Pakistani Taliban said it carried out the attack.
What about Sharif’s return?
Tensions across Pakistan intensified ahead of the arrival of the former prime minister in Lahore.
Clashes were reportedly broken between Sharif’s supporters and security forces on the main entrance to the city.