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 frustration was building among voters queueing at booths that failed to open on time.
Banda’s Movement for Multi-Party Democracy, which has run the nation since the end of one-party rule in 1991, claims most of its support in the countryside where farmers have benefited from a hugely successful agricultural subsidy scheme.
Sata’s strength is in the capital, Lusaka, and the northern Copper Belt, where many people complain about receiving meagre returns from more than five years of strong economic growth.
Banda, also 74, is due to vote in his constituency outside the capital this morning.
Voting is due to end at 1600 GMT and the first results from urban areas, where Sata and his Patriotic Front (PF) party look set to perform strongly, are likely to arrive late this evening.
Campaigning officially 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.
Banda appealed for a peaceful election on national television on Sunday night, and police are out in force to prevent any violence even though the southern African country of 13 million is not known for political unrest.