About 29 million Tanzanians head to the polls on Wednesday to elect new leaders with the world watching the big race pitting the opposition's Tundu Lissu against President John Magufuli.
In his address to the nation on Tuesday, President Magufuli urged Tanzanians to turn out in large numbers to exercise their democratic right, despite the arrest of opposition politicians in Zanzibar.
"Our campaigns have been conducted in an environment of peace and tranquillity," said the President. "Our security agencies did a commendable job," he added.
In Zanzibar, the main opposition party said Tuesday three people had been killed by police on the archipelago's island of Pemba, as clashes erupted ahead of Tanzania's elections.
Police fired teargas and live rounds, and brutally beat a young man in the opposition stronghold of Garagara as security forces began voting a day before presidential and parliamentary elections.
The opposition believes the special day of early voting is a ploy to steal the election on an island with a history of contested polls, and vowed they would try and vote on the same day.
Violence erupted on Pemba, an opposition stronghold, as the army distributed ballots which opposition supporters believed were pre-marked.
"Verified reports from Pemba in Zanzibar indicate that three citizens have been shot dead by the police using live ammunition," read a statement from the opposition ACT-Wazalendo (Alliance for Change and Transparency) party.
However, police dismissed the allegations. "We have not received any reports about such deaths and we do not expect anything of that nature," Inspector-General of Police Simon Sirro told reporters.
Speaking in Dar es Salaam, he said police were holding 42 people in Zanzibar over allegations of attacking officers distributing ballot boxes.
African Union Chairperson Moussa Faki Mahamat pleaded for peace and called for credible and inclusive elections.
"The chairperson calls for all stakeholders, political parties and their supporters to participate in the voting process peacefully and refrain from any acts of violence. He further urges the authorities to ensure a conducive environment to enable citizens to cast their votes in a safe and peaceful manner," Mr Faki's spokesperson said in a statement.
Former Nigerian President Goodluck Jonathan will lead a team of observers from the AU, while ex-Burundi President Sylvestre Ntibantunganya will lead 59 monitors from the East African Community.
The EAC will deploy teams in Dar es Salaam, Tanga, Lindi, Mtwara, Dodoma, Mbeya, Kigoma, Singida, Kilimanjaro, Morogoro and Mwanza regions and Zanzibar's twin Islands of Pemba and Unguja.
The ruling Chama Cha Mapinduzi has been in existence, and in power, since 1977, becoming Africa's second-longest ruling party. Although there are 15 presidential candidates this time, President Magufuli's strongest challenge comes from Lissu, even though he is expected to be re-elected.
But some observers have already found the electoral process skewed in favour of the CCM. "It is difficult to guarantee electoral justice in Tanzania in light of the prevailing legal and constitutional framework and context," the Tanzania Elections Watch,a virtual group of experts on the polls co-chaired by former Chief Justice Willy Mutunga and Ugandan legal experts, Frederick Ssempebwa and Ms Alice Mogwe, said.
"Ensuring electoral justice will require significant constitutional and legal reforms for which there has so far been no political will to embark on." Ahead of the polls, the government has been accused of either passing laws that impede fairness or retaining policies that favour CCM.
The National Electoral Commission (NEC) has a final say on presidential election results and no court challenge is allowed.
"It is not to say that an election becomes free and fair because of the positive comments of the observers. We do not think this election will be free and fair, not even if the opposition wins, against all odds. What we need are conditions of good governance in the entire election season," Prof Ssempebwa said on Thursday.
The NEC has accredited some 96 local and foreign organisations eligible for observer status, but it excludes major players like the Catholic Church and rights watch groups.
This will be first exercise since multiparty democracy with no support from the UNDP, after Dar refused to admit an assessment mission from the global agency.
"When we shut down political space, when we shut down civil space, we risk delegitimising those who govern us," argued Donald Deya, the CEO of the Pan-African Lawyers Union, warning the restrictions could fuel violence.