Voting concluded Wednesday in most of Zimbabwe’s polling stations in elections in which the country’s autocratic leader, Robert Mugabe, faced one of the biggest challenges to his 33-year grip on power.

A few polling stations were prepared to stay open into the night to accommodate all voters who were in line by 7 p.m. Ballot counting was expected to begin Wednesday night, and final results are expected by Monday.

Zimbabweans voted in large numbers despite concerns about the credibility of the electoral process, and the vote was relatively peaceful compared with the disputed and violent polls in 2008.

Thousands of voters lined up in Harare’s populous Mbare township, and polling officials said all were accommodated by the evening. “It’s a tremendous turnout,” said Magodelyo Yeukai, the presiding officer in Mbare.

Some election observers noted cases of registered voters being turned away from the polls. There have been worries about oversights in the hasty preparations for the vote, as well as fears of vote-rigging of the kind that allegedly occurred in past elections.

Tendai Biti, the third-ranking official in the former opposition party of Prime Minister Morgan Tsvangirai, Mugabe’s popular challenger, reported allegations of irregularities across several districts, including changes to voter lists and ballot papers.

But “we are encouraged by the high turnout. We remain confident in spite of all these challenges,” Biti said late Wednesday.

The head of the African Union election observer mission, former Nigerian president Olusegun Obasanjo, said reports of irregularities “will be investigated but have not yet been substantiated.”

Activists say a big turnout is likely to favor Tsvangirai, by blunting the effect of any manipulation of voter rolls. Mugabe, who barred Western observer missions, dismissed allegations of vote-rigging in the run-up to the polls as mudslinging by opponents.

Judge Rita Makarau, head of the election commission, reported “a few minor logistical problems” where voting started slowly and urged people to bring forward any evidence of irregularities.

Kadhashu Makanyanya was one of those who was unable to cast a ballot after he was told that his name was not on the voter rolls.

“I checked on the computer during the voter inspection, and it was there,” he said. “I am going to the command center now to check for my name.”

The Zimbabwe Election Support Network, a monitoring group, said it had observed potential voters with registration slips being turned away from the polls.

Mugabe, 89, has said he will step down if he loses. Many Zimbabweans are skeptical that the wily politician, a former guerrilla who led the country to independence in 1980 and has the backing of the security forces, would relinquish control if the vote didn’t go his way.

After casting his ballot in Harare’s western Highfield township, Mugabe said he expected to be reelected.

“We will have lots of things to do to get our economy back on its feet,” he said.

Tsvangirai, 61, who had been in an uneasy power-sharing arrangement with Mugabe, voted in northern Harare. “We have come to complete the change we have always fought for,” he said.

— Associated Press