Pakistan has been hit by violence on the day of its general elections – with at least 31 dead in the worst attack.

A man blew himself up outside a polling station in Quetta, in an attack claimed by the Islamic State group.

Preliminary, unofficial results suggest ex-cricket star Imran Khan’s PTI party is in the lead as votes are counted.

However, the rival party of disgraced former PM Nawaz Sharif, PML-N, has rejected the results amid allegations of vote rigging.

The campaign has been overshadowed by concerns of fraud and violence, and the Human Rights Commission of Pakistan says there have been “blatant” attempts to manipulate the polls.

According to unofficial initial results, the PTI party is currently leading in about 100 national assembly seats, while PML-N is ahead in about 60 seats, local media report.

However, only 20% of the votes have been counted so far, Dawn newspaper says.

The turnout has been estimated at between 50% and 55% out of 106 million registered voters, AFP reports.