(AFP) - Madagascar's outgoing president Andry Rajoelina launched his re-election campaign on Tuesday, promising "an orange wave" to thousands of supporters wearing his party colour who gathered in the capital, Antananarivo.

Voters in the Indian Ocean island nation will elect a president on November 9 but the run-up to the poll has been marred by tensions after disputes over its regularity.

For more than a week, opposition parties have held demonstrations against what they call an "institutional coup" to keep Rajoelina in power that have routinely been dispersed by police.

"Go to your towns, your districts, go throughout Madagascar to create an orange wave," Rajoelina, sporting orange trousers, sunglasses and a white shirt said, from a stage set up in a pine forest in the suburb of Akamasoa.

"No one will take the victory away from us," he told the crowd, which included rich, SUV-driving Malagasy as well as poor people living off scraps from a nearby dump.

The rally marked the start of the campaign period, but 11 of the 13 candidates in the running said on Monday they would abstain from campaigning until their grievances are addressed.

Rajoelina, 49, resigned last month in line with the constitution in order to run for re-election.

The president of the Senate, Herimanana Razafimahefa, was supposed to take over but declined for "personal reasons", leaving the task to a "collegial government" headed by the prime minister, an ally of Rajoelina.

The move was accepted by the country's top court, which also dismissed appeals to have Rajoelina's candidacy declared void over his dual French nationality, sparking opposition anger.

The 11 opposition candidates have since led almost daily, unauthorised marches in the capital, which have been met with a heavy police presence and tear gas.

Presidential hopeful Andry Raobelina, who was injured at a rally last week and later sought medical attention in the nearby island of Mauritius, has since filed a court appeal to have the elections postponed citing "force majeure".

In another development on Tuesday, Razafimahefa sent a letter to the Constitutional Court walking back on his decision to turn down the caretaker role.

"I am determined to assume my responsibilities," he told journalists, citing the "spectre of a political crisis" threatening Madagascar.

The United Nations on Tuesday expressed concern over the "deteriorating human rights situation" in Madagascar in the runup to the polls after "unnecessary and disproportionate force" was used to disperse protests.

"There should be clear instructions to the security forces to uphold the rights to freedom of expression, association, and assembly and to refrain from using disproportionate force -- to create an environment conducive to free, fair, and transparent elections," UN human rights office spokesman Seif Magango said in a statement.

Rajoelina first took power in 2009 on the back of a coup.

After not running in the 2013 election due to international pressure, he was voted back into power in 2018.

He has since held the reins in a country that remains among the poorest in the world despite vast natural resources.

© Agence France-Presse