The Southern Africa Development Community (SADC) cited cancellation of opposition rallies, biased state media and alleged voter intimidation among some of the issues that tarnished the election.
The observers deployed by the 16-nation SADC group, however said the period running to the election and the voting phases were “peaceful and calm”.
The poll is being watched across southern Africa as a test of support for 80-year-old President Emmerson Mnangagwa’s ZANU-PF party, which has ruled for 43 years.
Opposition, Citizens Coalition for Change (CCC), CCC leader Nelson Chamisa slammed the delays to vote as “a clear case of voter suppression.
Chamisa, 45, is the main challenger to Mnangagwa, 80, who came to power after a coup that deposed late ruler Robert Mugabe in 2017.