Buenos Aires (dpa/MIA) — The right-wing libertarian economist Javier Milei takes office as president of Argentina on Sunday, three weeks after the political outsider defeated the mainstream candidate with a promise to slash social spending and abolish the central bank.

The 53-year-old will be sworn in before giving his inaugural speech on the steps in front of the National Congress building in Buenos Aires.

He will then receive foreign leaders in the Casa Rosada, the presidential palace and seat of national government.

Spanish King Felipe VI, Chilean President Gabriel Boric, Uruguayan Prime Minister Luis Lacalle Pou, Paraguayan President Santiago Peña and Hungarian Prime Minister Viktor Orbán have announced their attendance.

Brazilian former president Jair Bolsonaro and the leader of the Spanish right-wing populist party Vox, Santiago Abascal, also plan to attend the ceremony.

Sunday also marks the 40th anniversary of Argentina's return to democracy after the military dictatorship.

Milei won the November 19 run-off election against former economy minister Sergio Massa.

During the campaign Milei - rocking a dishevelled mop of hair and often wielding a chainsaw - said he would introduce the US dollar as legal tender, abolish the central bank and many ministries, and drastically cut government spending.

He has since softened his rhetoric considerably and postponed or toned down many of his original plans. He also brought a number of experienced politicians into his Cabinet, whom he had previously vilified as members of the "caste" he despised.

Milei does not have a majority in parliament, leaving him reliant on other parties if he hopes to carry out major reforms.