Harare - Hundreds of Zimbabwean opposition supporters marched through the streets of Harare on Tuesday demanding electoral reforms and free and fair polls next month.

The opposition supporters were addressed by main opposition Movement for Democratic Change presidential candidate Nelson Chamisa, 40, before heading to the Zimbabwe Election Commission (ZEC) to hand over a petition calling for transparency.

"If ZEC want to hold a credible, free and fair election, we demand that all parties involved should know who is printing the ballot paper to avoid rigging," Chamisa said.

"If the voters' roll has not been audited by credible and an independent external auditor, there cannot be an election," he added.

Zimbabwe goes to the polls on July 30 with 75-year-old President Emmerson Mnangagwa, a veteran of the 1970s liberation war and previously a close ally of ex-President Robert Mugabe, the incumbent.

Mugabe was forced to resign during a military coup in November, after ruling the country for over three decades, during which there were numerous allegations of vote-rigging and intimidation.

Mnangagwa has promised these elections will be free and fair and has invited EU observers to monitor the vote.

But the opposition ZEC petition complained that state media has been biased towards the ruling party. It is also demanding no ex-military officials be allowed to work for the election body.

"We do not want soldiers to work for ZEC because they will not transfer power if the ruling party loses," said one protester 35-year-old Tinei Tinarwo.