Harare: Zimbabwe's main opposition leader said on Tuesday that his party had collected results from more than 10,000 polling stations, which showed it had done exceedingly well and was ready to form the next government.

Nelson Chamisa, 40, and 75-year-old President Emmerson Mnangagwa were the main contenders in Monday's election, the first since long-ruling Robert Mugabe was removed in a bloodless coup in November.

Several civil society groups are collating results in parallel with the Zimbabwe Electoral Commission (ZEC) but are not allowed to release results before the ZEC. A source at one group said it was too early to call a winner but it was looking "very close".

"Awaiting ZEC to perform their constitutional duty to officially announce the people's election results and we are ready to form the next government," Chamisa said on his official Twitter account on Tuesday.

Not to be outdone, Mnangagwa then said that the ruling party was receiving "extremely positive" information from their representatives. He said on Twitter that he was delighted by the high voter turnout, which the ZEC put at 75 per cent.

Electoral officials began counting votes after voting locations closed on Monday night amid opinion polls showing the winner was too close to call.

But with official results not expected to be known for days, the success of the election will be determined by whether rival parties accept them.

The poll's credibility is a key pillar needed to rebuild the southern African nation's international reputation and economy that was laid to waste under Mugabe's 37-year rule.

While voting officially ended at 7pm on Monday after a day marked by long, snaking queues in the capital, Harare, and other centres, some polling stations remained open to allow all those who had lined up to cast their ballots. Under Zimbabwean law, results must be announced by August 4. More than 5.6 million people registered to vote for president, 350 legislators and local government representatives.

"The people wanted to vote, they were in a very good mood to vote in most cases," Elmar Brok, chief observer for the European Union's observer mission, told reporters in Harare. While voting proceeded smoothly in some areas, in others it was "totally disorganised," and it was unclear whether this was a coincidence or bad organisation, he said.

The front-runners for the presidency are the ruling Zimbabwe African National Union-Patriotic Mnangagwa, Mugabe's one-time deputy and successor, and his main rival Chamisa, a lawyer and church pastor who heads the Movement for Democratic Change.

The MDC's campaign has made headway over the past two months, tightening the race "significantly," and if that trend continued victory could go either way, opinion polls conducted by research company Afrobarometer show.

The next ruler will have to administer an economy in meltdown after two decades of misrule and corruption under Mugabe, who the ruling party forced to resign in November, and a broke Treasury that's unable to service its loans or take out new ones. That will leave little scope to improve government services, rebuild crumbling transport links and meet a plethora of other election pledges.

"Zimbabwe's economy requires commercial bridge loans, donor support, relief on its huge dollar-denominated debt and, ultimately, an International Monetary Fund program," Exotix Capital said.

"A peaceful, free and fair election that is universally accepted as credible by foreign observers and establishes a strong enough political mandate domestically to commit to difficult fiscal cuts is the ideal outcome."

More than 6100 local and international observers were accredited to scrutinise the vote. There were no immediate reports of violence, said Andrew Makoni, chairman of the Zimbabwe Election Support Network, an association of 34 civil rights and religious organisations.

"It's the best election I have seen in Zimbabwe," said Ishmael Tsopotsa, 35, a metalworker who waited just a few minutes to vote in a tent on a dusty field in Mbare, a poor area of Harare. "No one is complaining. The results are going to be perfect."

The MDC was able to access rural districts that were once no-go areas, but it's still skeptical the election will be fair. Its complaints include that the voters' roll contains the names of dead and underage people, controls over ballot papers are inadequate and the electoral commission is biased in favour of the ruling party - allegations the body denies.

Mnangagwa has insisted the election would be credible.

"People finally got to say who they want, what they want," said Elton Ashely, 23, a student who served as a polling agent for the MDC in Mbare. "Now we need the final count from the Zimbabwe Electoral Commission. We just hope they will do the right thing."

Bloomberg News, Reuters