|President Rupiah Banda, centre, has presided over one of Africa's fastest growing economies [Reuters]
Stone-throwing mobs smashed cars and blocked roads during voting in Lusaka, Zambia's capital, after opposition leader Michael Sata accused President Rupiah Banda's rival camp of rigging the ballot.
But overall observers said Tuesday's voting proceeded smoothly in the presidential, legislative and local elections that will choose the next leader of one of Africa's fastest-growing economies.
Voting closed at 1600G amid tight security across the country, with first results expected late on Wednesday.
About 5.2 million registered voters were eligible to take part and the presidential race has been described by analysts as too close to call.
Both men contested the 2008 elections, which were marred by rioting after Sata rejected Banda's victory by two percentage points.
The polls were held after Levy Mwanawasa died before completing his term.
Banda has presided over one of Africa's fastest-growing economies thanks largely to the rising international price of copper, Zambia's main export.
But Sata has sought to turn the incumbent's economic track record against him by arguing that Banda has let foreign investors reap the rewards of the copper boom while ordinary Zambians continue living in poverty.
The election will decide the country's leadership for the next five years, but is unlikely to bring major policy shifts if Sata's Patriotic Front (PF) defeats the ruling Movement for Multi-party Democracy (MMD), in power for the past 20 years.
A PF win would only be the second transfer of power in Zambia since the country gained independence from Britain in 1964.
Closely fought election
The PF says if elected it will bring back a 25 per cent windfall tax on mining revenues that Banda's government abolished in 2009.
The increase in copper prices since then - from $3,000 a tonne to almost $10,000, and the friendly tax regime have drawn a rush of foreign and especially Chinese investment to Zambia.
Thanks largely to the mining boom, Banda has presided over an economy that grew 7.6 per cent last year and 6.4 per cent the year before.
But the PF says Banda has failed to spread the wealth, with 64 per cent of Zambians still living on less than two dollars a day.
Sata has also attacked his rival's record on corruption, after Banda's government refused to appeal the corruption acquittal of former president Frederick Chiluba, accused of embezzling $500,000 during his 1991 to 2002 presidency.
Eight other candidates are contesting the presidency.