Zambians voted on Tuesday in a closely contested election between President Rupiah Banda and opposition leader Michael Sata, who has been a critic of foreign investment in Africa's biggest copper producer, most notably from China.
Crowds of youths chanting We want change, we want change mobbed 74-year-old Sata as he visited a polling station in the capital, Lusaka, where long queues of people had to wait for hours for voting booths to open.
At one station, the frustration boiled over and the crowd went on the rampage, burning voting materials and damaging five vehicles.
Police said four people were arrested and election organisers later said voting in stations that opened late would be extended beyond the official 1600 GMT close to make up for lost time. First results from urban areas are likely to arrive late in the evening.
A European Union election observer in the country called the elections fair and peaceful.
The general impression is that the elections have been held in a correct and peaceful manner despite a few incidents of violence in Lusaka, Maria Muniz, the European Union's chief elections observer in Zambia.
In general, everyone who was entitled to vote has been able to vote, she said.
Banda's Movement for Multi-Party Democracy, which has run the landlocked nation since the end of one-party rule in 1991, claims most of its support in the countryside where farmers have benefited from an agricultural subsidy scheme.
Sata's strength is in Lusaka and the northern Copper Belt, where many complain about meagre returns from more than five years of pacey economic growth based on a global commodity boom.
I will vote for Sata because he's the only candidate who promises to address the issues facing the majority of Zambians, said Victor Mwanza, an unemployed 32-year-old.
Campaigning ended on Sunday for a 24-hour cooling off period after six weeks of mudslinging and rhetoric that sometimes touched on the growing clout of foreign mining firms in the $13 billion economy.
Banda, also 74 and widely known by his initials RB, cast his vote near his home town of Chipata, 600 km (400 miles) east of Lusaka, and urged Zambians to express their frustrations through the ballot box rather than on the streets.
Voting is louder than words, he told reporters.
Police are out in force to prevent violence even though the southern African country of 13 million is not known for political unrest.
Its kwacha currency has risen more than 3 percent against the dollar in the last week, suggesting investors are confident there will be none of the post-poll fighting that has blighted recent African elections from Ivory Coast to Kenya.
An opinion poll published a week ago suggested Banda held a narrow lead over Sata, nicknamed King Cobra because of his vicious tongue, although a number of floating voters meant an upset was still possible.
A large turnout of young voters, many unemployed, is likely to play into the hands of Sata, who lost to Banda by just 35,000 votes, or 2 percent of the electorate, in a 2008 presidential run-off.
Banda, a former diplomat and confidante of first president Kenneth Kaunda, has won accolades abroad for opening up the country to international investment and ensuring mining policies are clear and consistent.
Sata, whose career includes work in British car assembly plants, toned down his criticism of Chinese investment last week, telling Reuters on Friday that he would maintain strong diplomatic and commercial ties with Beijing if he won.
Chinese firms have become big players in the former British colony, with total investments by the end of 2010 topping $2 billion, according to Chinese embassy data.
Both men have pledged hefty spending on Zambia's woefully inadequate infrastructure, raising concerns about elevated government spending at a time of potential weakness in the price of copper, its economic mainstay.