Analysts are also divided over whether a win for Khan's would actually be that substantially different to a return to power for its chief rival, Pakistan Muslim League-Nawaz (PML-N), the party of disgraced former Prime Minister Nawaz Sharif.
"This is not an election, it is selection - to install someone of your own choice and to topple others", Mushahid Hussain Sayed, a senior PML-N leader, said at the press conference with Sharif.
The country is mid-way through election day.
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.
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The vote is proving to be a close fight between Khan's Pakistan Tehreek-e-Insaf (PTI) party and the Pakistan Muslim League-Nawaz (PML-N), led by jailed former Prime Minister Nawaz Sharif.
Results will start trickling in within hours, and the likely victor should be known by around 2:00am on Thursday.
Early voting was heavy at some polling stations in Islamabad, the capital, and the Punjab provincial capital, with several political party leaders standing in line to cast their ballots.
Pakistanis were voting Wednesday in a historic third straight election ending a campaign marred by widespread allegations of manipulation that local and global rights group have said imperil the country's wobbly transition to democratic rule. Media footage showed disabled people arriving to vote across the country, and one news channel followed the election experiences of a team of wrestlers and two grooms who left their weddings to cast ballots.
Election officials say delays in releasing the results are simply down to technical failures in the electronic reporting system and the votes are now being counted manually.
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According to the unofficial estimates, almost 48 per cent polling was recorded in Pakistan, which is 7 per cent lower as compared to 2013.
"This is the first time in Pakistan's history that five political parties have called a foul play in the polls and termed them massively rigged", he said.
At least 32 people were killed and several injured mostly in a suicide bombing in Balochistan on Wednesday as millions of voters queued up across Pakistan to elect a new government.
"Now the army, the intelligence agencies and the judiciary are taking sides", said PML-N voter Tariq Ateeq Sheikh, 50, a property dealer in Lahore's Walton neighbourhood.
According to a survey conducted by Dawn.com earlier in the week, Imran Khan's Pakistan Tehreek-e-Insaf (PTI) has been touted as the front-runner in the forthcoming elections.
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She says the two drifted apart after she was diagnosed with multiple sclerosis in 2008. " I think she's single, I think he's single ".
Sharif warned his party would launch protests against the alleged rigging.
He said that in case any proof is brought forward, action will be taken against all individuals found involved.
According to the Election Commission of Pakistan (ECP), 3,459 candidates are contesting for 272 general seats of the National Assembly, while 8,396 candidates are running for 577 general seats of the four provincial assemblies - Punjab, Sindh, Balochistan and Khyber-Pakhtunkhwa. The PTI and ruling PML-N are thought to be neck and neck in the elections.
More than 19 million new voters, including millions of women and young people, may prove decisive.
Jibran Nasir, an independent candidate from the financial hub of Karachi, said he received death threats and even had a fatwa, or religious edict, issued against him.
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To form a government without a deal with one of the other parties, they will need to claim a total of 137 seats.