Argentina's libertarian economist Javier Milei took office and warned in his maiden speech that he had no alternative to a sharp, painful fiscal shock to fix the country's worst economic crisis in decades, with inflation heading towards 200 per cent.

Milei, 53, a former TV pundit who shot to fame with expletive-ridden tirades against rivals, China, and the pope, is taking over from Peronist leader Alberto Fernandez, whose government was dogged by failures to rein in soaring prices.

Javier Milei warned there was no alternative to a fiscal "shock" in his maiden speech after being sworn into office on Sunday, saying his predecessors had left the country without funds and on a path to hyperinflation.