ZANZIBAR: Tanzania's semi-autonomous Zanzibar archipelago went to the polls on Sunday amid ramped-up security in a re-run of disputed elections that have been boycotted by the main opposition party. Zanzibar's electoral authority annulled a previous ballot on Oct. 25 on grounds of fraud. The opposition Civic United Front (CUF) says it won those elections and it has warned of violence on the Indian Ocean islands if Sunday's ballot goes ahead. The CUF has urged its supporters to boycott the presidential, parliamentary and municipal elections in a move that could mean a shoo-in for the ruling CCM party. Other smaller opposition parties are taking part in the vote, but elections are usually tight two-horse races between the CCM and CUF. Security was tight around polling stations. Zanzibar elections have previously been marred by violence. 'Polling stations in all the seven constituencies in our district opened at 7 am (0400GMT) and voting is going on smoothly. People are turning out to cast their ballots peacefully in good numbers,' Maalim Khamis Mussa, an election supervisor in the Zanzibar West B district told journalists. Authorities temporarily banned passenger ferry services between the semi-autonomous islands and mainland Tanzania on Sunday, in what officials said was a move aimed at making sure there were no disruptions to voting. President Ali Mohamed Shein of the ruling CCM party stood in the previous polls against his main challenger, Seif Sharrif Hamad of the CUF party, who has lost four elections since 1995 by narrow margins. The Zanzibar Electoral Commission said there are around 500,000 registered voters in the election, with final results expected to be announced within three days of voting.