Zambians are heading to the polls on Tuesday in what is expected to be a close presidential election rematch between incumbent Rupiah Banda and opposition leader Michael Sata.

President Banda hopes to ride a wave of recent economic success to defeat Mr. Sata, a passionate nationalist leader – nicknamed “King Cobra” – who heads Zambia's main opposition Patriotic Front.

President Banda says his policies promote economic growth, while Mr. Sata accuses the president of allowing corruption and of granting too much power to foreign investors, mainly China, a major operator of Zambian copper mines.

Mr. Banda and his Movement for Multiparty Democracy narrowly defeated Mr. Sata in a 2008 run-off election to replace the late President Levy Mwanawasa, who had died of a stroke. Mr. Sata disputed the results, and his supporters rioted for days afterwards.

Mr. Sata recently urged his supporters to “defend” their votes by remaining at polling stations after casting their ballots. He has accused the electoral commission of planning to rig the presidential poll using pre-marked ballot papers. The commission has dismissed the allegations.

The semi-official Times of Zambia says election officials have demanded that those who place their votes must immediately leave the polling centers.

Zambian officials have stepped up security around voting centers, banning street vendors from selling liquor and tools such as axes or shovels that could be used as weapons. Officials have warned that any violence will be met with the “full force of the law.”

More than 5.1 million Zambians are registered to vote in the presidential, parliamentary and local elections. Multiple international election monitoring agencies are on hand to observe the election process.