Imran Khan stands on the brink of being the next prime minister of Pakistan, with the former playboy and cricket legend's PTI party enjoying a strong lead in early results.

Counting the ballots from Wednesday's election has proved much slower than expected, but with nearly 50 per cent of polling stations reporting Mr Khan's party was leading in 113 of the 272 national constituencies.

It puts him far ahead of the incumbent Pakistan Muslim League - Nawaz (PML-N) party of jailed former premier Nawaz Sharif, on 64 seats, but also short of the outright majority needed to govern without a coalition.

Mr Khan's party spokesman, Fawad Chaudhry, tweeted "Congratulations to the nation on a new Pakistan! Prime Minister Imran Khan", although his party has officially held off on declaring victory.

That may come in a speech Mr Khan is due to deliver at 4pm this afternoon (local time), set to be broadcast live.

And while the official results are still trickling in, PTI supporters are not waiting to celebrate what they see as Mr Khan's victory. Throughout the night, Khan supporters celebrated outside party offices countrywide.

Dawn, Pakistan's leading independent newspaper, declared that PTI appeared to be sweeping the board across the country and that "we are on the brink of a new Pakistan". PML-N's performance, according to polticial commentator Asha’ar Rehman, gave "the impression of a party which was faced with its toughest hour and which was on the verge of collapse".

Supporters of the jailed prime minister Sharif seized on the delays in the counting process, calling it an assault on democracy in a country that has a history of military rule.

Election officials said the demand of counting the ballots of up to 105m registered voters had caused the electronic system to break down, meaning they were now being counted by hand.

"There's no conspiracy, nor any pressure in delay of the results. The delay is being caused because the result transmission system has collapsed," said Election Commission of Pakistan (ECP) secretary Babar Yaqoob.

But early on Thursday, Mr Sharif's brother Shehbaz, who now leads the PML-N, rejected the results amid further complaints that soldiers stationed in polling stations had thrown out poll monitors from political parties during the counting.

"It is a sheer rigging. The way the people's mandate has blatantly been insulted, it is intolerable," Shehbaz told a news conference as the counting continued.

"We totally reject this result," he said. "It is a big shock to Pakistan's democratic process."

The Pakistan People's Party (PPP), led by the son of assassinated two-time prime minister Benazir Bhutto, was ahead in 42 constituencies and, as expected, appears to have secured third place.

A progressive party compared to the conservatism of both the PML-N and PTI, they have vowed not to enter coalition with either of the main frontrunners - once a major party, analysts said they would be best placed to rebuild for 2023.

The PPP also denounced the validity of PTI's imminent victory, saying its polling agents were asked to leave during the vote count in a number of voting centres.

"This is the warning bell of a serious threat," said PPP senator Sherry Rehman. "This whole election could be null and void, and we don't want this."

If he does indeed become Prime Minister, it will be because Mr Khan was able to both secure the support of establishment institutions and also a broad spectrum of followers with sometimes troubling populist messaging.

The 65-year-old has courted the more extreme wings of Pakistan’s religious spectrum by touting the death penalty for blasphemers and vowing to implement an “Islamic welfare state” if he comes to power.

Yasir Yusuf, a 33-year-old chef from the capital’s small and downtrodden Christian minority, cast his vote just before polls shut at 6pm on Wednesday evening.

He told The Independent he had decided to vote for PTI despite concerns about Mr Khan’s perceived tolerance for extremist Islamist parties.

“We are concerned, but when you are a minority you become meaner; we just think for ourselves,” he said.

“We are too little and this country is too big. I really want to vote for my country, not only for this small minority.”

​Asim Majeed, a 24-year-old MBA student, complained of “how slow the people are in there” as he emerged from casting his vote for PTI in Islamabad. He said he believed Mr Khan was different from other leaders.

“We have seen people like Nawaz Sharif,” he said. “[Khan] is a new person so we can believe that he can bring some change in the country.”

A profile on his PTI party's website says Mr Khan was a "quiet and shy boy in his youth" and attended the Royal Grammar School, Worcester, before completing his formal schooling with an undergraduate degree in economics from Keble College, Oxford.

He was captain of the Oxford University cricket team in 1974, before going on to an illustrious sporting career, leading his country to victory in the 1992 World Cup.

His profile says: "The party has Islamic overtones and is inspired partly by Imran Khan's renewed commitment to Islam.