Zimbabwe's leading opposition party, the Citizens Coalition for Change (CCC), said the voters' roll made available for public inspection by election authorities seemed to be riddled with "errors."
"We have noted serious anomalies," the CCC said.
Some voters' names were missing while others had - unknowingly to them - been registered to vote in places other than their ward of residence, it said.
CCC lawmaker David Coltart, a former education minister, said he was among those who could not find their name on the list at his local polling station.
"Whether it is chaos or whether it is deliberately targeting CCC members, we cannot say at the moment, but one can only describe the voters' roll as shambolic," Coltart told AFP.
He later tweeted that, after a day of trying, he found his name registered at a polling station further away from his home.
Hundreds of people reported similar issues, he said.
Zimbabweans head to the polls in what is predicted to be a tense general vote later this year, with the ruling party accused of cracking down on opposition voices.
President Emmerson Mnangagwa has said a date for the elections - expected to be in August - would be announced this week.