Madagascar's President Andry Rajoelina was sworn in on Saturday for a third term after being declared winner of last month's presidential election, and vowed to pursue industrialisation and unity in the Indian Ocean island country.

Rajoelina, 49, first came to power in a 2009 coup. He stepped down in 2014 but became president again after winning the 2018 election.

"I will be the president who unites all Malagasy people," Rajoelina told thousands of his supporters at the swearing-in ceremony in the capital Antananarivo, that was also attended by six heads of state.

"We will take particular care of the poor, the elderly, women, young people and children. For the next five years, we will pursue three pillars: human capital, industrialization and improving the management of public administration."

Rajoelina got 58.96% of the votes cast, while the runner-up, lawmaker Siteny Randrianasoloniaiko, got 14.39%, according to the country's High Constitutional Court which declares final results.

Randrianasoloniaiko and other contenders have rejected the results of the poll, which they say was marred by irregularities including intimidation of polling officials and use of public resources by the ruling party.

The election was preceded by weeks of protests, with the opposition saying Rajoelina should not have run because he acquired French nationality in 2014 - which they say automatically revokes his Malagasy one - and had created unfair election conditions.

They also demanded the polls be postponed and asked Rajoelina to first appoint independent officials to the electoral body.

Ten out of 13 candidates subsequently boycotted the poll after the government refused to implement their demands but their names remained on the ballot.

The opposition described the voter turnout, at 46.35%, as the lowest in the country's history.