Tanzania's new president, John Magufuli, was sworn in Thursday, despite continuing disputes over the October 25 election.
Magufuli and Vice President Samia Suluhu Hassan took the oath of office in front of cheering crowds at Uhuru Stadium in the capital, Dar es Salaam.
In a short speech, Magufuli promised to work hard to implement the pledges he made during the campaign.
The election extended the longtime rule of the CCM party both in the presidency and in parliament.
The opposition says the presidential election was rigged and has rejected the results, while the semi-autonomous Zanzibar region annulled its polls because of alleged irregularities.
European Union election observers said the polls were well organized but said a lack of transparency undermined the opposition's trust in the electoral process.
Magufuli is Tanzania's fifth president since the country won independence from Britain in 1961. Unlike many African countries, Tanzania has a history of peaceful transfers of power. President Jakaya Kikwete stepped down this year after completing two terms in office.
Magufuli defeated his main challenger Edward Lowassa in last month's election 58 to 40 percent, according to official results.
The new president is 56 years old and spent 15 years in the government's Cabinet, mostly as minister of works, whose job is to oversee construction projects.
During the campaign, he pledged to reduce unemployment and poverty in Tanzania and improve infrastructure. Tanzania is one of the poorest countries in Africa, where according to the World Bank, nearly half the population lives on less than $2 per day.