Election officials reported high turnout in the polls which were marred by violence in opposition stronghold of Zanzibar where opposition protestors were hurt in clashes with police.
Many streets in the commercial capital of Dar es Salaam were empty and businesses were deserted of city residents who are among nearly 16 million eligible voters.
Many had to wait in long lines to cast ballots.
On the mainland, officials and foreign election observers reported only minor logistical snags.
"The process went well," said one monitor from Britain. "Everybody had a chance to vote despite small hitches here and there."
At least 12 people were wounded and dozens arrested as police battled opposition supporters.
One man was shot when security forces fired live rounds over the heads of demonstrators, another was stabbed, and seven people, including an opposition candidate and a police officer, were beaten in melees, they said.
The clashes in Zanzibar occurred when supporters of the opposition Civic United Front (CUF) tried to block allegedly bogus voters from casting ballots for the ruling Revolutionary Party (CCM).
Police, who were patrolling the Stone Town, barred journalists and observers from entering halls where ballots were being counted, telling they are not needed, according to an AFP correspondent.
While the ruling party only narrowly won Zanzibar's polls, it is widely expected to cruise to victory in the national elections due to its large backing on the mainland.
Retiring Tanzanian President Benjamin Mkapa, who is constitutionally barred from seeking a third term, said he believed Foreign Minister Jakaya Kikwete, to succeed him.
"I am sure my party's candidate will be elected like I was in 2000," Mkapa told reporters after voting outside Tanzania's commercial capital of Dar es Salaam.
Campaigning ended on a dramatic not on Tuesday after the Mr Kikwete, the presidential frontrunner, collapsed from exhaustion at his final political rally.
Voters are choosing a new president, a 232-seat parliament and local officials in Tanzania's third elections since political pluralism was introduced in 1992 that the rulling party is heavily favored to win.
"I came here and voted for CCM because everybody in my family is a member," aid Dar es Salaam voter Neema Hassan.
Despite the long odds, the CUF and 16 other opposition parties are hoping to capitalize on public unhappiness with corruption and endemic poverty to pick up seats in the legislature.
At the presidential level, Kikwete looms large over his nine competitors, including the two main opposition candidates Ibrahim Lipumba of the CUF and Augustine Mrema of the Tanzanian Labor Party, according to analysts and polls.