The campaign launch of the CITIZENS Coalition for Change (CCC) in Chiredzi was blocked by the police on Wednesday, citing a clash with a State occasion.
The opposition party had planned to hold a rally in Tsvovhani Stadium, but the police said they had no resources to cover both events.
The State occasion was the official opening of a clinic by Minister Ezra Chadzamira, the Minister of State for Provincial Affairs and Devolution Masvingo Province.
This is the latest setback for the CCC, which has been struggling to kick off its campaign ahead of the general elections on August 23.
The party has accused Zanu PF of using State institutions like the police to sabotage its rallies in rural areas.
CCC leader Nelson Chamisa is challenging President Mnangagwa, who has been on a campaign spree, seeking re-election.