Madagascar's coup leader Colonel Michael Randrianirina was sworn in as president on Friday, after the military took power in the island nation this week following youth-led protests that forced Andry Rajoelina to flee.

Rajoelina, whom lawmakers impeached after he fled abroad at the weekend, has condemned the takeover and refused to step down despite widespread defections in the security forces.

The African Union and the United Nations Secretary-General Antonio Guterres have condemned the coup, which came after weeks of "Gen Z" protests.

"I will fully, completely, and justly fulfil the high responsibilities of my position as President of the Republic of Madagascar," Randrianirina said in a ceremony at the High Constitutional Court.

"I swear that I will exercise the power entrusted to me and dedicate all my strength to defending and strengthening national unity and human rights," he added.

Randrianirina said earlier that the military had taken power and dissolved all institutions except the lower house of parliament, or National Assembly.

He also said that a committee led by the military would rule for up to two years alongside a transitional government before organising new elections.

Randrianirina was a commander in the elite CAPSAT army unit that played a role in the 2009 coup that brought Rajoelina to power but broke ranks with him last week, urging soldiers not to fire on protesters.

Madagascar's population of about 30-million people has an average age of less than 20 years. Three-quarters of the people live in poverty. Between its independence in 1960 and 2020, GDP per capita plunged 45%, according to the World Bank.