Sharif's brother Shehbaz, who now leads the Pakistan Muslim League-Nawaz (PML-N), rejected the count after complaints soldiers stationed in polling stations had thrown out political parties' monitors during the tabulations.
Imran Khan's spokesperson Naeemul Haque said that the PTI chief will "address" Pakistan on Thursday at 2 pm PST, reported Dawn, "in celebration and recognition of the massive support received from the people of Pakistan in the 2018 elections which was a contest between the forces of good and evil".
With 42 per cent of polling stations counted, the Election Commission of Pakistan had Mr Khan's Pakistan Tehreek-i-Insaf (PTI) party leading in 113 of 272 contested National Assembly constituencies, according to Pakistan's Dawn Newspaper.
PML-N alleges the country's powerful military - which has ruled Pakistan for roughly half of its 70-year history and has often sparred with Sharif over control of security and foreign policy - is behind a campaign that tilted the electoral playing field in favour of Khan's PTI. The 2013 election was also marred by violence, with 150 people killed in the six weeks leading up to polling day.
Millions of voters will choose between candidates including cricket legend Imran Khan who leads the Pakistan Tehreek-e-Insaf (PTI) and the Pakistan Muslim League-Nawaz (PMLN) spearheaded by Shehbab Shariff.
Pakistan was locked in tense election race Wednesday, pitting cricketer-turned-politician Imran Khan against the party of jailed former prime minister Nawaz Sharif in a process disrupted by a suicide bomb that killed at least 31 people near a polling station. Final results are expected early Thursday. The Pakistan People's Party (PPP) of Bilawal Bhutto was third.
Early voting was heavy at some sites in Islamabad and also in the Punjab provincial capital, with several political party leaders lining up to cast ballots.
The election has been beset by allegations of fraud and violence.
"This is the most important election in Pakistan's history", Mr Khan, 65, said after casting his vote in the capital Islamabad.
However, in a bid to silence the pre-poll rigging reports, the CEC of Pakistan has given his assurance to people that the election body is trying really hard to hold unbiased elections.
"We will sweep the elections", said Abdul Basit, who watched the results on a large TV screen.
People of Pakistan went to the polls to cast their vote on Wednesday with social media quick to react to the events of the day.
He said that in case any proof is brought forward, action would be taken against all individuals found involved.
The Americans will be particularly concerned about the outcome of the election, given that Khan famously said he would order the Pakistani military to shoot down American drones if he came to power, and advocated negotiations with Pakistani Taliban fighters rather than military operations against them.
As per the Election Commission, at least 3,459 candidates are in the fray 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.
As well as expressing anti-US views, Khan has promised to build a 'model Islamic welfare state, ' create 10 million new jobs and stamp out corruption, despite being accused by opponents of engaging in corrupt activity himself.
Meanwhile, PML-N's Murtaza Abbasi is leading with 31,320 votes in NA-15 Abbottabad, while PTI's Ali Asghar has garnered 25,460 votes. "We know all the other candidates and parties". Polling was halted at the polling station.