Bomb blasts in Karachi, Peshawar and Balochistan kill 12 people and injure dozens more as millions of voters head to the polls.
A dozen people have been killed and more than 50 injured in several bomb blasts across Pakistan as the nation goes to the polls.
Two deadly attacks in the port city of Karachi hit the political offices of the Awami National Party, one of three secular liberal parties targeted by Taliban militants during the run-up to the historic elections. The twin bombs left 11 dead and wounded 37 others.
In Peshawar, a bomb planted on a motorbike targeting women voters injured eight, while a suicide bomber targeting another polling station in the region blew himself up without injuring anyone else after he was spotted by police and prevented from entering the building.
There were two more blasts in the remote Nasirabad district of Balochistan, with one person reported dead and seven wounded.
Campaigning ahead of the vote was also marred by deadly violence.
More than 130 people were killed in bombing and shootings ahead of the landmark elections and Taliban militants vowed to disrupt the democratic process by targeting polling booths.
The leader of the Pakistan Taliban claims democracy runs counter to Islam.
Millions of voters are heading to the polling booths in the election, which could upset the dynamics of traditional politics in the nuclear armed country.
Pakistan's political system has until now revolved around the powerful dynasties of the Bhuttos and the Sharifs.
The main parties - the outgoing Pakistan People's Party (Bhutto - led by President Zardari) and the frontrunner Nawaz Sharif's Pakistan Muslim League-N - have ruled the country a total of five times in the past 25 years.
But there is a disruptive new old kid on the block: the internationally famous playboy cricketer turned political superstar Imran Khan.
Imran Khan has been around on the political scene for an aeon but has only really become a force in the last few years gaining what he calls a "tsunami of support".
Mr Khan has struck a chord with his message of change and with his extremely critical comments of the United States' use of drone strikes.
They have caused profound anger across Pakistan.
By emphasising "change" though he has managed to tap into the frustrations of millions of Pakistanis - especially urban middle class youth - who believe traditional politicians are corrupt to the core.
For him, more than the others, turnout will be crucial especially among the youth.
Almost half of Pakistan's more than 80 million registered voters are under the age of 35.
At this stage it is unclear whether his genuine support will translate into a large number of seats but some believe he may be the kingmaker in the next parliament even becoming Pakistan's next Prime Minister.
"I think it is the most unpredictable election Pakistan has ever had," said Moeed Yusuf, South Asia adviser at the United States Institute of Peace.
"The two-party dominance has broken down, and now you have a real third force challenging these parties."
The vote is also a boost for Pakistan's credentials as a democratic country.
It is the first time in its 65-year history that a civilian government has completed a full term.
Previous administrations have always been toppled by military coups or sacked by presidents in cahoots with the army.
And there have been further indications that the army is staying very much on the sidelines of this election.
Early this morning pictures of the chief of the military, General Ashfaq Kayani, casting his vote were shown on Pakistan's multitudinous TV networks.
It is a signal that the army is respecting the democratic process.
The vote is also being watched closely abroad.
In Washington who wins will be seen as crucially important for the fight against global terrorism and the NATO mission in Afghanistan.
Mr Khan and Mr Sharif are both close to the religious right and have been accused of being soft on the Pakistan Taliban based in the tribal areas bordering Afghanistan.
Some analysts believe a strong showing for either may be problematic for NATO forces.
Its soldiers are planning on exiting Afghanistan via Pakistan next year.