Officials started counting the results in Zambia after polling stations closed on Thursday as voters waited in long lines to cast their ballots.
The Electoral Commission of Zambia said that over 83% of the country's eligible voters, amounting to more than 7 million people, registered to vote in the elections at more than 12,000 polling stations.
A high turnout was reported in the capital Lusaka and other regions of the southern African nation, despite a tense atmosphere.
Both President Edgar Lungu and his main rival Hakainde Hichilema had billed the election as a test of Zambia's democracy stability.
Although both men urged people to vote peacefully, violence flared up between supporters of Lungu's Patriotic Front party and Hichilema's United Party for National Development.
President Lungu voted early on Thursday and urged people to stay at home and "wait patiently and peacefully for the outcome".
"I hear some politicians are advocating for people to hang around the polling centres, that will just bring chaos,'' said Lungu.
"I have voted. I am going home and will listen to the radio, newspapers, television and wait for the results to be declared. That's what a good citizen does. Please don't hang around polling stations, you will just cause unnecessary anarchy," he added.
Internet access to several social media platforms has been restricted in what looks like a government attempts to stop people talking about the vote until official results are announced.
Such internet restrictions have become common during many elections in African countries.
Results will be announced on Sunday at the latest, the electoral commission said earlier this week, with expectations for the vote to be closely fought between the two men, like previous contests in 2015 and 2016.
If none of the 16 candidates vying for presidency gets more than 50% of the votes cast, it will go to a second-round vote.
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