This in a presidential election that ran into a second day after heavy rains disrupted voting.
Results from 14 out of 150 constituencies showed defence and justice minister Lungu, 58, had 103,634 votes, compared to 47,731 for his main rival, Hakainde Hichilema, 52, a wealthy economist from the United Party for National Development (UPND).
Much of the southern African country was lashed by heavy rain during election day and a handful of polling stations that could not open will hold voting on Wednesday, the election commission said.
Voter turnout was “very low” at around 34 per cent for the constituencies where ballots had been counted and the final result may be announced later than Friday, it added.
However, the kwacha gained one per cent against the dollar to 6.49 as the peaceful vote eased investor jitters about stability in Africa’s second biggest copper producer.
With another election due late next year when President Michael Sata’s term would have ended had he not died in office, the winner will have little time to turn around a stuttering economy in one of Africa’s most promising frontier markets.
Zambia has averaged six to seven per cent growth as the mining sector boomed but that slowed to 5.5 per cent last year, the International Monetary Fund says, and could ease further with the price of copper reaching a six-year low this month.
(READ MORE: Zambia on path of recovery)
Lungu, a former lawyer with a laid-back, populist style, has used his campaign to tap into the grassroots support of his predecessor, who died in October aged 77, prompting this week’s by-election.
Hichilema, one of Zambia’s wealthiest businessmen, has said if he wins he will draw on his experience in the private sector to attract foreign investment and diversify an economy where copper accounts for 70 per cent of export earnings.