Campaigning ended at midnight with impassioned pleas for votes from frontrunner Nawaz Sharif, a steel tycoon bidding for a historic third term as prime minister, and cricket star Imran Khan looking for a breakthrough.
The main outgoing Pakistan People's Party (PPP) has run a lacklustre and rudderless campaign in the face of Taliban threats and with its chairman, Bilawal Bhutto Zardari, too young to contest a parliamentary seat.
Attacks on politicians and political parties have killed more than 120 people since mid-April, according to an AFP tally, and the Human Rights Commission of Pakistan said the elections were the most violent in the country's history.
It said its acute concern did not stem merely from threats and violence targeting individuals "but much more from the manner in which the violence has already impaired the fairness of the elections almost beyond repair".
It called on all institutions to "stretch themselves to their absolute limit to ensure security of voters, candidates and polling stations on Saturday so that the people can exercise their right to choose their representatives".
Most commentators expect Sharif's centre-right Pakistan Muslim League-N (PML-N) to win but it remains unclear how far Pakistan Tehreek-e-Insaf (PTI) can provide an upset and restrict his chances of forming a stable coalition.
As the countdown to the polls began, the election commission announced that 179 million ballot papers were being distributed to around 70,000 polling stations across the country under army supervision.
More than 600,000 security personnel, including tens of thousands of soldiers, have been ordered to deploy to guard against attacks on polling day.
On Friday, a motorbike bomb killed four people and wounded 15 close to offices of different parties in the main town of North Waziristan, the premier stronghold of the Taliban and Al-Qaeda-linked groups on the Afghan border.
Security officials said PML-N, PTI and right-wing religious party Jamiat Ulema-e-Islam, an ally of the outgoing government, had offices nearby.
Witnesses and officials said 15 people were taken to the state-run Miranshah hospital, some of them in a serious condition.
The device detonated when supporters of former cabinet minister and PPP national assembly lawmaker Sardar Omar Gorgaj were gathering in his office.
Saturday's polls are the first time in Pakistan's turbulent history that an elected civilian administration has handed power to another through the ballot box. The nuclear-armed state has been ruled by the military for half its life.
More than 86 million voters have from 8am to 5pm to elect 272 lawmakers to the 342-member national assembly and lawmakers to four provincial assemblies.
No one claimed responsibility for Friday's bombings, but the Taliban, who consider the election un-Islamic, have carried out numerous attacks to undermine the polls and say they have dispatched suicide bombers for polling day.
The Taliban have singled out the secular-leaning PPP and its main coalition partners, the Muttahida Qaumi Movement, which controls Pakistan's biggest city of Karachi, and the Awami National Party in the northwest.
On Thursday, a son of former PPP prime minister Yousuf Raza Gilani was kidnapped and two of his aides killed in the central city of Multan.
Gilani told reporters on Friday that there had been no claim of responsibility for the abduction of his son, Ali Haider Gilani, a 27-year-old PPP candidate for the assembly in Punjab province.
"We should create a conducive atmosphere for the elections, so that polls look fair and transparent," Gilani said.
Gilani was disqualified after being sacked and indicted by the Supreme Court last year for refusing to reopen corruption cases against the president, but has been openly campaigning on behalf of three of his sons.
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