No one immediately claimed responsibility, but local officials were quick to blame the Islamic State group.
Baluchistan also saw the deadliest suicide bombing in the run-up to election day, with 149 people, including a provincial assembly candidate, killed at a campaign this month.
The election has been beset by allegations of fraud and violence.
Former global cricket star and socialite Imran Khan is confident that a victory in Pakistan's general elections on Wednesday will kick start a revolution for a country bedeviled by corruption and insecurity.
The Pakistan Peoples Party (PPP) of former president Asif Ali Zardari was leading in 32 seats, a sign indicating that he could play a "kingmaker" in case of a hung parliament, according to media reports.
Sharif, 68, was removed by presidential decree in 1993, in a military coup in 1999, and previous year by the Supreme Court, which ordered his corruption trial.
Officials have confirmed that 32 people have died and 35 have been wounded.
"Whatever way elections run, I see a lot of instability", said defence analyst Ayesha Siddiqua, who authored Military Inc, a look at the extensive financial holdings of Pakistan's army.
A Pakistan Tehreek-e-Insaf (PTI) worker was killed and two others injured as party activists clashed with Awami National Party (ANP) workers outside a polling station in Nawan Kali in Khyber-Pakhtunkhwa's Swabi.
People line up at a polling station during the general election in Karachi, watched by a soldier.
Hottest day of the year 2018
During the current heatwave, United Kingdom temperatures have been approximately 10C higher than average for this time of year. The Met Office predicts that temepratures will hit at least 37C in parts of the United Kingdom during Friday.
Pakistan is locked in a close and tense election race on Wednesday, pitting cricket hero Imran Khan against the party of jailed ex-Prime Minister Nawaz Sharif in a process marred by a suicide bomb that killed 31 people near a polling station. That attack was also claimed by Islamic State militants.
"We support free, fair, transparent and accountable elections in Pakistan, as we do around the world; and we encourage all Pakistanis to peacefully exercise their democratic right to vote", the spokesperson said.
The 85,307 polling stations opened at 8am local time and continued for 10 hours, an hour longer than in the 2013 polls.
With tensions already high, shooting broke out between supporters of rival parties in the northwestern city of Sawabi, leaving...
Pakistan's military deployed 350,000 troops countrywide at polling stations.
"This is a deplorable and cowardly attack on a day when voters across Pakistan should be casting their ballots in a peaceful environment, without fear or hindrance", Michael Gahler, the EU's chief observer to Pakistan, said.
Though the recently held opinion polls showed PTI an inch ahead in the National Assembly contest from the PML-N, both the parties are pinning hopes to get maximum number of seats from Punjab, who has the highest number of 141 National Assembly seats.
With just 30 percent of the total vote counted, the Election Commission of Pakistan had Khan's Pakistan Tehreek-i-Insaf (PTI) party leading in 113 of 272 contested National Assembly constituencies. Voting for two parliamentary seats and six seats in provincial assemblies has been postponed due to attacks on candidates or disqualifications.
Polls have now closed across the country, and initial results are expected early Thursday.
"A lot has been written dismissing Pakistan's election as a sham but there are scores of women, grandparents and great grandparents queuing today to cast their vote even in the face of news of violence from Quetta", said Fahd Humayun, a researcher at Jinnah Institute. "We will take action", Yaqoob said.