Elsewhere, minor blasts and clashes between party workers left several injured and one dead.
Voters are deciding between the parties of the former cricket star Imran Khan and the disgraced former Prime Minister Nawaz Sharif.
But the campaign has been overshadowed by concerns of fraud and violence.
The Human Rights Commission of Pakistan says there have been "blatant" attempts to manipulate the polls.
Despite tight security across the country, with more than 370,000 troops deployed to secure the ballot, violence has broken through.
(BBC News )