Nearly 305,000 Zimbabwean voters were turned away and 206,000 received assistance from election officials during last week's disputed vote, the state-appointed election commission says.
Thursday's revelation followed reports by independent poll monitors of widespread manipulation of the voters' roll and irregularities in the elections that President Robert Mugabe won with 61 percent of the vote.
Morgan Tsvangirai, Mugabe's challenger, won 34 percent of the vote and has called the elections "fraudulent". He said he would seek legal redress.
The Zimbabwe Electoral Commission said nearly 3.5 million people cast their ballots in the July 31 polls, which extended Mugabe's 33-year rule and ended a unity government formed in 2009 in which Tsvangirai was prime minister.
The commission's statistics showed the largest number of voters - 64,483 - were turned away in the capital Harare.
Urban areas have long been a stronghold of Mugabe's rival Tsvangirai.
Regular voters were reportedly turned away because their names were missing from the voters' roll, they were registered in another ward or they did not have adequate identification.
The Zimbabwe Election Support Network (ZESN) said over 750,000 urban voters were missing from the electoral list, in what they described as "a systematic effort to disenfranchise an estimated million voters".
"A total of 99.97 percent of rural voters were registered while only 67.94 percent of urban voters were registered," said Solomon Zwana, chairman of ZESN.
Rights groups say police forced some people they believed to be opposition supporters to feign illiteracy and seek the assistance of police officers or polling officials, with their votes going to Mugabe.
Zimbabwe has the highest literacy rate in Africa.
The country's former finance minister, Simba Makoni who defected from Mugabe's ZANU-PF in 2008, joined those voices rejecting the outcome.
"We reject the results announced by ZEC as not free, not fair, not credible and not legitimate," said Makoni.
"These results do not reflect the expression of the free will of the people of Zimbabwe."
Makoni, the leader of the Mavambo Kusile Dawn party, had backed Tsvangirai in the elections.
He complained about the lack of availability of the voters' roll in time for the polls and the high number of ballot papers that were printed above the registered voters.
"Hundreds of thousands of potential voters failed to register and were therefore denied their right to vote. This point has a significant bearing on the outcome of the election," he said.
Meanwhile, the high court refused bail on Thursday for Tsvangirai's delegate to the ZEC who had reported dumped ballots after security forces voted early on July 14 and 15.
Morgan Komichi was detained just days before the general elections because he would not reveal his source for the dumped ballots.
"So it's back to square one. Circumstances have changed and we will approach the magistrate's court with a fresh bail application next week," said his lawyer Andrew Makoni.
Komichi was already denied bail a first time last week.