The whereabouts of the presidential candidate for Zanzibar for the opposition party ACT-Wazalendo (Alliance for Change and Transparency) Seif Sharif Hamad remains unclear after he was reportedly arrested on Tuesday morning in Garagara, the island of Pemba.
Mr Hamad was expected to take part in the early voting at the Garagara polling station.
The general election is slated for Wednesday on the Tanzanian mainland and the semi-autonomous Zanzibar island.
But Zanzibar Electoral Commission had designated Tuesday as a special day for early voting for security forces and election clerks. The opposition, which has been against early voting over concerns that it is a ploy to rig the election, called on its supporters to also vote on the same day.
According to AFP, violence erupted in Garagara, an opposition stronghold, where police fired teargas and live rounds, and brutally beat a young man.
ACT-Wazalendo said in a statement that three people had been shot dead and nine others injured.
"Verified reports from Pemba in Zanzibar indicate that three citizens have been shot dead by the police using live ammunition," read the statement by ACT-Wazalendo.
Police are yet to comment on the whereabouts of Mr Hamad.
Mr Hamad, 77, faces the ruling Chama cha Mapinduzi (CCM) presidential candidate for Zanzibar Hussein Mwinyi.
Dr Mwinyi, 53, is the Minister for Defence and National Security of Tanzania and the son of Tanzania’s second president Ali Hassan Mwinyi.