After a tediously slow count, Pakistan election officials on Friday announced Khan's Pakistan Tehreek-e-Insaf (PTI) party won 109 of the 269 seats being contested in the National Assembly.

Imran Khan's supporters began celebrating his victory in Karachi on Thursday night by dancing in the street and setting off fireworks.

The election on Wednesday gave his nearest rival, Shehbaz Sharif's Pakistan Muslim League, 63 seats. Sharif, who heads the party of jailed ex-prime minister Nawaz Sharif, has rejected the results charging widespread fraud and manipulation.

Khan declared his victory on Thursday and dismissed the allegations of fraud calling it the most transparent election in Pakistan's history.

Third place went to the left of centre Pakistan Peoples Party (PPP) with 39 seats. Results from 20 seats were still being counted.

The 65-year-old Khan has disparaged liberals, attacked feminism, embraced radical religious parties and vowed to uphold Pakistan's blasphemy law.

He enjoys the support of the country's powerful military establishment, although he has been known to go his own way.

Khan has led his Pakistan Tehreek-e-Insaf party, or PTI, in widespread protests alleging ballot-rigging in the 2013 election, in which he received about 19 per cent of the vote.

He also has seized on an anti-corruption message and led demonstrations against former Prime Minister Nawaz Sharif, demanding a criminal investigation after leaked documents from a Panama law firm revealed that Nawaz Sharif and his family had undisclosed assets abroad.

He went on hunger strike in jail after being picked up at a banned rally in 2007.