Argentina's new President Alberto Fernandez briefly swapped duties on Friday, returning to unfinished business at his former job as a college professor overseeing students' final exams.

Fernandez, sworn in on Tuesday, surprised students when he showed up to supervise an exam in his crime and justice class at the University of Buenos Aires, where he was a law professor before launching his presidential bid this year.

Heavy security lined the halls of the law school after Fernandez, 60, arrived by car from the Casa Rosada presidential palace. Dressed in a suit and tie, he sat patiently at the front of his classroom while his students took their hours-long final. When it was over, they posed for a group photo.

"He's no longer a candidate for president, he is the president of the nation. It's historical. This will never happen to me again in my life," said student Nadina Tatiana Pasanini.

Fernandez, little-known in the South American country until earlier this year, had kept up his college professor duties during the presidential campaign, culminating in his October 27 triumph against conservative Mauricio Macri, who had been seeking re-election for a second term.

In September, Fernandez traveled to Madrid to teach university classes, an obligation he said he committed to before announcing his candidacy. He had continued to oversee exams until October, when the presidential elections took place.

The brief return to his days as a college professor comes ahead of a crucial moment for Fernandez's administration as he prepares to navigate Argentina out of a severe financial crisis and a looming debt pile that must be renegotiated with global bondholders and the International Monetary Fund.

Fernandez, who won strong support amongst younger voters, has looked to underscore his credentials as a man of the people, including social media post of him playing the guitar and taking his brown and white collie Dylan to vote.

The center-left Peronist also drove himself to his own inauguration in his silver Toyota sedan, waving to the crowds that lined the streets from the driver's side window.