Patriotic Front (PF) Presidential candidate Edgar Lungu and his wife Esther Lungu leave a rally in Lusaka January 19, 2015. Lungu's rapid rise from backroom politician to presidential front-runner in one of Africa's most promising frontier markets has revealed tactical nous and a steely determination that few knew lay beneath his quiet exterior. Zambians go to the polls on January 20, 2015 following the death of President Michael Sata in October 2014. [Photo/Agencies]

The central business district of Lusaka, the Zambian capital, was quiet as people cast ballots before heading to work.

The main presidential contenders are Edgar Lungu of the ruling Patriotic Front party and Hakainde Hichilema, leader of the opposition United Party for National Development.

Lungu, in charge of Zambia's justice and defense ministries, is portraying himself as a candidate for continuity, saying he wants to complete economic development projects initiated by Sata. Hichilema, an economist, counters that he has the necessary experience to revamp the economy of Zambia, a major copper producer.

Zambia has been led since Sata's death by acting President Guy Scott, a white Zambian of Scottish descent who is not a candidate. Scott was not entitled to become president under Zambian law because his parents were not Zambian or of Zambian descent.

The southern African nation has 5.1 million registered voters in a total population of about 15 million. The winner of the election will serve out the remainder of Sata's term until elections next year.