A turn out of well over 50 per cent of the country's four million voters had been expected by electoral officials on Thursday and those still queuing after polls officially closed at 6pm would still be allowed to cast their vote.
Dan Kalale, the Zambian director of elections, said: "Voter turnout has been huge and very encouraging."
The incumbent president, Levy Mwanawasa, 58, seeking a second and final five-year term, is facing four other candidates. The most serious threat to his tenure is likely to come from Michael Sata, a populist from the Patriotic Front party.
A former cabinet minister known as "King Cobra", Sata split from Mwanawasa's ruling Movement for Multiparty Democracy before the 2001 general election which was marred by allegations of fraud.
If elected, he says he might follow the example of Robert Mugabe, the president of neighbouring Zimbabwe, and stand up for Zambia against international economic forces.
He has accused Mwanawasa of "selling out" Zambia to Western donors and foreign firms, particularly from China, which are interested in the country's copper reserves.
Sata is a populist who accuses
the government of selling out
As he cast his vote in the capital, Lusaka, he said: "Mugabe hasn't done anything wrong. It is the imperialists."
Despite rising tensions before the poll and hints of possible rigging charges from Sata's Patriotic Front, Thursday's voting went off smoothly across most of the country.
Kalale said there were only a few hitches involving undelivered ballots, which were later rectified when voting papers were sent in by helicopter.
Mwanawasa, a lawyer who made his mark with an anti-corruption drive targeting Patrick Chiluba, the former president, wants to highlight an economic record which has seen Zambia win $7 billion in debt relief from Western donors, cut poverty and push economic growth above five per cent.
He has repeatedly said that this election is a "critical" referendum on Zambia's economic future.
But he lacks Sata's common touch, and appeared grim as he cast his vote at a rural precinct. He declined to speak to reporters, and was in such a hurry he almost left the first lady behind.