The polls have generated a lot of interest and come after an acrimonious campaign during which the opposition accused the ruling side of muzzling its voice.
Zimbabweans are casting ballots in parliamentary and local authority by-elections — seen as a yardstick of what is to come in next year's general polls.
The polls, which opened at 7:00 am on Saturday, have generated so much interest that President Emmerson Mnangangwa has led various campaign rallies to shore up support for ruling ZANU-PF candidates.
"We need change," Jasen Maeka, a 42-year-old unemployed man said after voting at a polling station in central Harare.
"We should give the opposition a chance. This government has proved to be a failure," Maeka said.
Opposition leader Nelson Chamisa, who is seen as the most formidable challenger to Mnangangwa, formed a new party Citizens Coalition for Change (CCC), three months before the by-elections.
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Complaints of repression
The ZANU-PF, which has led the country since independence from Britain in 1980, attracted huge campaign crowds.
On the other hand, Chamisa's party complained of growing repression by the authorities as several of its events were banned by the police during the two-month long campaign.
Unrest at an opposition rally last month left one person dead and 22 injured.
Critics accuse Mnangagwa, who took power in 2017 after Robert Mugabe ruled for 37 years, of muzzling dissidents and the opposition has voiced concern that election will not be credible.
Voters are casting ballots in 28 parliamentary constituencies including 20 where opposition lawmakers were recalled in a battle over the control of the country's largest opposition party.
By-elections were also being held in 122 local government municipalities. Sixteen parties were taking part in the elections.
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