Ex-cricket star Imran Khan has taken an early lead as votes are counted in Pakistan's national election, but his rivals allege major vote-rigging.

Early unofficial results suggest his PTI party is in the lead, but it will need to form a coalition if it is unable to secure a simple majority.

Results are trickling in slowly, but election officials deny rigging, saying there are simply technical problems.

Voting day saw bloodshed, with many killed in a blast at a polling station.

This historic election will mark only the second time that a civilian government has handed power to another after serving a full term in Pakistan.

With 42% of polling stations reporting, the Election Commission of Pakistan had Mr Khan's Pakistan Tehreek-i-Insaf (PTI) party leading in 113 of the 272 National Assembly constituencies being contested, according to Pakistan's Dawn Newspaper.

But the party of disgraced former Prime Minister Nawaz Sharif has weighed in rejecting the results, as have a host of smaller parties, all alleging vote-rigging and manipulation.

"The way the people's mandate has blatantly been insulted, it is intolerable," Shehbaz Sharif, leader of the PML-N and brother of the former prime minister Nawaz Sheriff. (BBC)