With just 30 per cent of the total vote counted, the Election Commission of Pakistan had Mr Khan's Pakistan Tehreek-i-Insaf (PTI) party massively leading in 119 of 272 National Assembly constituencies.

Mr Sharif's Pakistan Muslim League-Nawaz (PML-N) was ahead in 61 constituencies, and the Pakistan Peoples Party (PPP), led by the son of assassinated two-time prime minister Benazir Bhutto, led in 40 constituencies.

An official at the Election Commission said early on Thursday that final results had been delayed by technical failures. "There's no conspiracy, nor any pressure in delay of the results. The delay is being caused because the result transmission system has collapsed," secretary Babar Yaqoob told reporters.

Mr Khan's camp was increasingly confident of winning the election, although it still appeared likely to fall short of the 137 seats needed for a majority in the National Assembly, raising the prospect it would need to find coalition partners among smaller parties and independents. The party's supporters took to the streets to celebrate the lead.

Mr Sharif's brother Shehbaz, who now leads the Pakistan Muslim League-Nawaz (PML-N), rejected the count of the Pakistan election results after complaints that soldiers stationed in polling stations had thrown out political parties' monitors during the tabulations.

"It is a sheer rigging. The way the people's mandate has blatantly been insulted, it is intolerable," Shehbaz Sharif told a news conference as the counting continued. "We totally reject this result... It is a big shock to Pakistan's democratic process," he said.

Elections in Pakistan took place this time under the allegations of manipulation by the army and concerns over participation of terrorist and radical groups. The race was mostly a two-way one, between former cricketer Imran Khan's Pakistan Tehreek-e-Insaf and jailed former prime minister Nawaz Sharif's Pakistan Muslim League-Nawaz.

More than 30 political parties fielded candidates for the elections to the 272 seats of the lower house of parliament, the National Assembly; 8,396 candidates are running for 577 seats in four provincial assemblies -- Punjab, Sindh, Balochistan and Khyber-Pakhtunkhwa. Nearly 10.6 crore people are registered to vote.

An unprecedented 460 candidates from terrorist and radical groups are in fray, which has raised concerns in India. The leading among them are candidates from Mumbai-terror attack mastermind Hafiz Saeed-led banned outfit Jamat-ud Dawa. Saeed's son and son-in-law are contesting the elections.