Argentines are choosing a new president in an election rocked by the emergence as front-runner of anti-establishment populist and self-styled "libertarian" Javier Milei. Mr Milei is an outspoken right-wing economist whose "shock-jock" style and aggressive social media campaigning have appealed to younger voters. His victory in the primary has put his two main rivals on the defensive. The election comes amid a severe economic crisis.