The opposition Movement for Democratic Change (MDC) and Western nations have denounced Friday's poll as rigged.
An observer mission from the Southern African Development Community (SADC) had been expected to give the vote a clean bill of health, as it has done in previous elections that the opposition said were fixed by President Robert Mugabe's ZANU-PF.
"The picture that emerged at the close of the poll was an election day which was peaceful. Notwithstanding these initial observations, the SADC elections observer mission is concerned with the number of people who were turned away from polling stations," the observers said in a statement.
Electoral officials said about 10% of voters had been turned away in six of Zimbabwe's 10 provinces either for lacking proper identity documents or being at the wrong voting centre.
An independent monitoring group put the figure as high as 25%.
"It is still not clear to us exactly how many people were affected in this way as well as the reason for them not being able to cast their votes," the SADC mission said.
SADC adopted new electoral guidelines last year which have induced Mugabe's government to institute electoral reforms.
"It is also the mission's view that although there were efforts to ensure equitable access to the public media, there is still considerable room to improve in this area and to allow access to the state media by the opposition," the SADC mission said.
"Furthermore, there were allegations by a number of stakeholders [concerning] the use of food and as an electoral tool which we were unable to confirm," added the group.