There are long queues outside polling stations, as Zambians vote in what is expected to be one of the country's tightly contested elections. President Rupiah Banda is expected to face his strongest challenge from Michael Sata. Since the last vote in 2008, an extra one million people have registered to vote - many young and unemployed. High copper prices have boosted economic growth but many ordinary Zambians say they have not benefited. Thousands of policemen have been deployed to prevent violence and the sale of axes and other potential weapons has been banned during the election period. Mr Banda defeated Mr Sata by jut 35,000 votes in the last election, sparking rioting by some opposition supporters in their urban strongholds. Some 5.2 million people - the highest on record - have registered to vote in these presidential, parliamentary and local elections. Polls opened at 06:00 local time (04:00 GMT) and will close at 18:00, with the first results expected late on Wednesday. 'Vote-rigging claims' Some polling stations have opened late due to a shortage of polling material but Chief European Union election observer in Zambia Maria Muniz De Urquiza said these problems had mostly been solved. "So far, the reports we have is that everything is going in a peaceful manner, in a calm way," she told the BBC. The BBC's Mutuna Chanda in Lusaka says the queues stretch for 2-3km in some of the polling stations he has visited. On the eve of the vote police chief Francis Kabonde said his officers would arrest anyone carrying axes, machetes and other weapons. The election commission said it was confident the polls would be free and fair. "What the commission has put in place is really a transparent system where there will not be any space or chance for anyone to manipulate," commission spokesman Chris Akufuna told reporters. Earlier, Mr Sata's the Patriotic Front (PF) accused Mr Banda's Movement for Multi-Party Democracy (MMD) party of trying to steal the vote. The PF alleged that the MMD had tried to bus in people from neighbouring Malawi to vote in an attempt to bolster its chances of winning. The PF said it had blocked the bus from entering Zambia but the MMD denied it had been involved in any attempt to rig the elections. Eight other candidates are contesting the presidency. Mr Banda has campaigned on a platform of infrastructure development and economic growth, largely spurred by Chinese investments and the government's decision to scrap a windfall tax of 25% on mining companies. Mr Sata has promised to re-introduce the tax and to promote policies that will bring greater benefit to poor people. More than 60% of Zambians live on less than $2 a day.