Polls in Zambia closed at 6:00 pm (1600 GMT) Tuesday, but election officials said hours would be extended at stations that opened late in a tumultuous day of voting that saw riots erupt in the capital.

Zambians are choosing their leaders for the next five years in the presidential, parliamentary and local elections, but many polling stations opened after the official 6:00 am start time, some because election materials were delivered late.

The Electoral Commission of Zambia (ECZ) said voting hours at all stations that opened behind schedule would be extended by the same amount of time as the delay.

All voters still in the queue at closing time will be allowed to cast their ballots, ECZ said in election materials distributed to journalists.

The election pits pro-business President Rupiah Banda and the ruling Movement for Multi-party Democracy (MMD) against fiery nationalist Michael Sata, leader of the country's largest opposition party, the Patriotic Front (PF).

Voting was troubled by violence in poor neighbourhoods around Lusaka, where angry residents burned buses, smashed cars belonging to election officials and threw rocks at police.

National police spokeswoman Ndandula Siamana said calm had returned to the city by mid-afternoon.

She said five people had been arrested and charged with conduct likely to cause a breach of peace and malicious damage to property.