The winner faces the formidable task of matching Mwanawasa’s strong record of fiscal discipline, praised by Western donors, and of cracking down on corruption. Mwanawasa died from a stroke in August after leading Zambia out of an economic slump.
His main challenger Michael Sata, leader of the opposition Patriotic Front, portrays himself as a champion of the poor.
Polling stations opened as scheduled at 6 am (0400 GMT), with some voters in Lusaka lining up several hours early. There was a light police presence in and around the capital ahead of the voting.
"From what is going on, the turnout is going to be very good. There is a lot of interest generated in this election and some people were here as early as 3:30 am (0130 GMT)," said Patrick Chokochani, 46, a presiding officer at a polling station in the city.
But there were complaints that voter registration cards were missing at least one polling station.
The polls were due to close at 6 pm (1600 GMT) and results were not expected until Friday.
NO DRAMATIC CHANGES
The only published opinion poll, released by the African market information group Steadman, showed Banda with 32 percent support compared to 46 percent for Sata, who narrowly lost the 2006 presidential election to Mwanawasa.
Both candidates have vowed to take on the nation’s major challenges, including poverty and an AIDS epidemic.
Sixty-five percent of Zambia’s 12 million people live on less than $1 a day and more than a million are HIV-positive.
Banda is hoping to benefit from Zambia’s relative prosperity as well as Mwanawasa’s enduring popularity. Zambia’s economy has grown at an average of 5 percent per year since 2002, boosted by a sharp rise in world commodity prices.
Inflation has fallen from more than 200 percent in 1991 to its current rate of about 14 percent.
Those successes are music to the ears of middle class voters, who may be the key to the election. Sata had difficulty making inroads with this group in the 2006 election, with some voters turned off by his strident populism.
"I voted for someone who shows respect to the people and has a good economic programme for the country," said Benjamin Musonda, a 32-year-old electrical engineer and Banda supporter, at a polling station in a Lusaka suburb.
Popularly known as "King Cobra" for his political manoeuvring, Sata has built a political base among the poor and working class, lashing out in the past at foreign investors, particularly those from China.
During the recent campaign he tempered his anti-investor stance and drew big crowds in rural areas, suggesting his party had expanded beyond its traditional base among labourers in Zambia’s Copperbelt region and Lusaka.
"There is too much poverty and unemployment," Harrison Mwale, a 33-year-old domestic worker, said as he prepared to vote for Sata.
Although the vote is seen as a test of Zambia’s commitment to multi-party democracy, restored in 1990 after 18 years of one-party rule under Kenneth Kaunda, neither Banda nor Sata is expected to dramatically reshape the political landscape.
Zambia’s army chief said on Wednesday that election-related violence would not be tolerated. A senior intelligence official said troops would be placed on high alert after the close of voting to prevent unrest.