This is in what shaped up as a tight race between a populist lawyer and a wealthy economist.
Edgar Lungu, leader of the ruling Patriotic Front (PF), is seen having a slight edge over main rival Hakainde Hichilema, a businessman whose United Party for National Development has won over the middle-class and investors.
With no reliable opinion polls, few experts are keen to call a clear winner in the contest to succeed President Michael Sata, who died in office in October aged 77.
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Lungu's campaign has focused on tapping into the grassroots support base of Sata, a populist leader from the majority Bemba tribe who won over the working class by funding infrastructure projects in poor, rural areas.
Hichilema, one of Zambia's wealthiest businessmen known locally as "HH", says his experience in the private sector will help him encourage foreign investment and diversify the southern African state's copper-dependent economy.
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Zambia, the continent's biggest copper producer after Democratic Republic of Congo, has been one of the world's best performing economies in the last decade, averaging 6-7 per cent growth as the mining sector boomed.
But growth slowed to 5.5 per cent last year, the International Monetary Fund says, and could ease further with the price of copper, which accounts for 70 per cent of export earnings, falling to a 6-year low this month.