Zimbabwe's President Emmerson Mnangagwa on Wednesday told over 150,000 supporters in the capital of Harare they would be "lost" if they did not re-elect him at this month's tense polls.

"If Harare fails to vote Zanu-PF, you will be lost," the 80-year-old strongman said as he addressed a rally for his party Zanu-PF near the city centre.

"No one will stop us from ruling this country," he said at the party's first major rally in the capital.

Zimbabwe votes on August 23 to elect the president and legislature in what analysts expect to be a tense affair, amid a crackdown on dissent and a disaffected population battling hyperinflation, poverty and high unemployment.

Suspicions over possible election irregularities are rife in a nation that has been ruled by the same party since independence in 1980 and has a long history of disputed votes.

Over 100 buses were organised to ferry people from different provinces for the occasion.

Supporters were given lunch packs and party regalia at the venue.

Some street vendors from the Mbare township in Harare told AFP they were forced to down their tools and told to board buses headed to the rally.

Mnangagwa will for a second time face off against Nelson Chamisa, a 45-year-old lawyer and pastor who heads the country's largest opposition party the Citizens Coalition for Change (CCC).

At the party's manifesto launch on Tuesday evening, Chamisa accused Zanu-PF of "resorting to dirty tricks" because the party was in "panic mode".

The CCC is stronger in disaffected urban areas while Zanu-PF is banking on a strong showing in its rural strongholds, observers say.

Mnangagwa accused Chamisa of promising Zimbabweans aid from Washington in exchange for votes.

"Every country" was "developed by its own people, it's shameful that Chamisa wants Zimbabwe to be developed by Biden," he said.

Ahead of his speech, Mnangagwa unveiled a borehole which was drilled at the site.

The president has been on a ribbon-cutting spree in recent weeks in an effort to reassure voters about the state of the economy and his governance.

Last week he opened a coal mine, clinic and a coal-fired power plant that he said would go a long way in easing electricity shortages.

Dubbed "The Crocodile" for his political cunning, Mnangagwa won a violence-stained election with 50.8 percent of the vote at the last polls in 2018.

"There are... negative people outside the country who want us to be violent," he said, adding, "Peace remains our beacon".