In a few areas, voting was extended to allow those still in queues to cast their ballots, officials added. Four opposition groups are backing one candidate, former Prime Minister Edward Lowassa.
"I went to the polling station very early in the morning ready to cast my vote", Emanuel Motta, a voter from Arusha in northern Tanzania, told Anadolu Agency.
Outgoing President Jakaya Kikwete, who will step down after serving two terms, has urged against violence.
Lowassa, the 62-year-old former premier leading the opposition presidential bid, quit CCM in July after the party spurned him as their candidate.
"Police also confiscated computers and mobile phones of our volunteers who were tallying results of the presidential election", John Malya, a Chadema lawyer said.
In the run-up to the polls, the opposition has accused CCM of using state institutions to rig elections and intimidate its supporters, something the party and the government deny.
Hamad, 71, claims to have seen official documents of final voting figures, although there has been no announcement from the electoral commission and the figures could not be verified.
Tanzanians head to the polls Sunday and the election is the primary topic of conversation these days.
Other candidates for the presidential seat are Anna Mghwira of Alliance for Change and Transparency (ACT), Hashim Rugwe of Chama cha Ukombozi wa Umma (CHAUMMA), Lutalosa Yembe of Alliance for Democratic Change (ADC), Janken Malik of National Reconstruction Alliance (NRA), Tanzania Labour Party's (TLP) Machmillan Lyimo and United People's Democratic Party (UPDP).
Polls and analysts forecast a presidential victory for John Magufuli, a CCM candidate. Most recently, the 62-year-old served as prime minister of Tanzania until 2008, when he was forced to resign amid allegations that he lobbied the government to extend an energy contract.
"The teargas was part of a campaign of fear... and intimidation to stop people celebrating", CUF official Ismail Jussa said.
The Civic United Front, another opposition party, said police had fired tear gas at a crowd of its supporters in Tanzania's Indian Ocean island of Zanzibar.
"The ongoing presidential results being announced by the National Electoral Commission are deeply flawed", Chadema Chairman Freedom Mbowe said, noting that the party did not recognize the results being released. Lowassa, on the other hand, defected to Chadema after he was allegedly removed from CCM's nomination list but in his campaign trail, has been categorical that his leadership will turn around how the country is run.
"I want a lasting peace and work for my children", said Bintou Coulibaly, a trader casting her ballot in a neighbourhood of the commercial capital, Abidjan.