The elections have attracted 15 presidential candidates from 15 political parties, but the race is tight between incumbent President John Magufuli of the ruling party Chama Cha Mapinduzi and Tundu Lissu from leading opposition Chama Cha Demokrasia na Maendeleo.
Magufuli is seeking re-election to serve his second and final five-year term to complete what he describes as his agenda aimed at making Tanzania an economic powerhouse.
Most of the polling stations opened at 7 a.m. local time and are expected to close at 4 p.m. with each station accommodating less than 500 voters.
Magufuli arrived at Chamwino polling station and cast his ballot at around 10 a.m. in the capital Dodoma.
"Today is an important day for Tanzanians to practice and strengthen democracy," Magufuli said in a statement televised by state-run Tanzania Broadcasting Corporation.
He encouraged registered voters to elect their leaders of choice, and appealed to Tanzanians to continue cherishing the country's peace and tranquility during the elections.
Semistocles Kaijage, the chairman of National Electoral Commission, said on Tuesday the electoral commission was the only authorized body to announce election results but did not say when the results would be released or when the new president would be sworn in.