Radical Islamic terrorist group Islamic State (IS, formerly ISIS) claimed responsibility for the deadly blast, according to the group's propaganda outlet, the Amaq News Agency.
Baluchistan also saw the worst violence during election campaigning earlier this month, when a suicide bomber blew himself up at a political rally, killing 149 people, including the candidate Siraj Raisani.
Just over a decade after the end of Pakistan's most recent era of military rule, Wednesday's vote features competing narratives of democracy amid Sharif's accusations elements of the powerful army are working to throw the race to Khan, which he denies.
Another PML-N veteran is likely to taste dust as PTI's Ali Haider Zaidi is ahead of former finance minister and Nawaz Sharif loyalist Miftah Ismail by 2,183 votes from NA-244 (Karachi East-III seat).
Khan's party spokesman, Fawad Chaudhry, tweeted "Congratulations to the nation on a new Pakistan!" The Human Rights Commission of Pakistan has said that there are "ample grounds" to doubt the legitimacy of the election, a view echoed by Sharif, who described his arrest as motivated by "blind revenge" and said upon his return to Pakistan "what credibility is now left of the elections?" As the results trickle, it will be clear in a few hours as to who will be the next Prime Minister of Pakistan.
He asked candidates to name a particular polling station and an appropriate action would be taken next.
According to reports in Pakistan media, it has been a fierce battle between jailed former prime minister Nawaz Sharif's Pakistan Muslim League-Nawaz (PML-N) and cricketer-turned-politician Imran Khan's Pakistan Tehreek-i-Insaf (PTI) in Punjab. Another 400 people were injured in the attack, which was claimed by IS.
Supporters of Imran Khan, chairman of the Pakistan Tehreek-e-Insaf (PTI), political party celebrate during the general election in Islamabad, Pakistan, July 26, 2018.
However, the ECP in an instant decision rejected the request and announced that whosoever will be in the premises of the polling stations or in the queue till 6 pm would be allowed to cast the vote after the deadline.
Also Wednesday, shooting between supporters of two opposing political parties killed one person and wounded two in a village near the northwestern city of Swabi.
More than 105 million people registered to vote in this election, at 85,000 polling stations.
At another polling station, Samra Aslam, 53, said she was voting for Sharif because he had brought development to the country.
Khan's PTI party has inched ahead of PML-N in recent national polls, but even if it gets the most votes, it will likely struggle to win a majority, raising the prospect of weeks of haggling to form a messy coalition government.
Security fears did not appear to deter some voters in the eastern city of Lahore a day before the election.
Almost 10.6 crore people are registered to vote for members of the lower house of parliament and four provincial assemblies.
Polls have now closed across the country, and initial results are expected early Thursday.
Pakistan's election commission reminded candidates their elections will be nullified if the female voter turnout didn't reach 10 per cent.
Voting began at 8 am (local time), during which most of Pakistan's almost 106 million people came out to cast their votes.
"We made history today", said Mohamad Ayaz Khan, a government administrator. Here are highlights of polling in Pakistan today.
Worldwide and domestic election observers will monitor the voting. A further 70 seats for women and minorities are awarded proportionally based on the voting percentages.
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