Makoni took his election campaign to the Zimbabwean capital after a senior politburo official in Mugabe's ruling ZANU-PF, Dumiso Dabengwa, threw his weight behind the former finance minister on Saturday.

"We know there are government employees who woke up to see huge sums of money in their accounts which did not appear on their pay slips," Makoni told a rally of about 3,000 people.

"We know there are civil servants who were embedded in (party) structures for campaigning to re-elect one party."

Millions of Zimbabweans hoping for an end to an economic crisis are expected to vote in the presidential, parliamentary and municipal polls described by Mugabe and his opponents as a landmark poll in the post-independence period.

Makoni is standing as an independent after being expelled from ZANU-PF and Mugabe also faces Morgan Tsvangirai, a long time rival from the main opposition Movement for Democratic Change (MDC).

Analysts say Makoni poses one of the biggest political challenges Mugabe has ever faced but the opposition's failure to unite behind one candidate could work in his favour.

The MDC says Mugabe has fraudulently won previous elections and unleashed violence against opposition supporters.

Mugabe, in power since independence from Britain in 1980, denies the charges and says the vote will silence the opposition and shame Western critics who accuse him of rights abuse.

"People will refuse to be intimidated. We will not accept intimidation to stop us from fighting for our freedom," said Makoni in a stadium in volatile Highfield township, where security forces have cracked down on dissent.

"With Simba Makoni a new Zimbabwe is born," read one placard.

Makoni, a reform-minded technocrat who has long been touted as a possible successor to Mugabe, promised to end what he called a climate of fear.

"Why is it that the government claims that people are on their side?," he said, suggesting Zimbaweans were too scared to defy their leader.

Mugabe rejects blame for daily hardships marked by the world's highest inflation rate of over 100,000 percent, high unemployment and food, fuel and foreign currency shortages.

He says Western powers working with the opposition have sabotaged the economy in retaliation for his policy of seizing white-owned commercial farms to resettle landless blacks.

Makoni said he would not give land back to whites if elected but would take action against Zimbabweans who took control of several farms, unlike Mugabe, who he accused of supporting the abuse of land reforms started in 2000.