Leftist Lopez Obrador sworn in as Mexico president

Andres Manuel Lopez Obrador was sworn in as Mexico's next president Saturday, after the anti-establishment leftist won a landslide election victory promising to "transform" a country fed up with crime, poverty and corruption.

The leader, widely known by his initials as "AMLO," begins his six-year term with strong majorities in both houses of Congress -- but has caused market jitters in Latin America's second-largest economy with a style that some see as authoritarian and radical.

"I swear to defend the constitution of the United Mexican States and its laws, and faithfully and patriotically carry out the post of president of the republic that the people have entrusted to me," Lopez Obrador said with his right hand raised before the Congress.

Lopez Obrador is vowing to lead a sweeping "transformation" after 89 years of government by the same two parties.

Not everyone is persuaded by the brand of change he is promising: critics accuse the sharp-tongued, silver-haired leader of being an authoritarian radical, and Mexican stocks and the peso have plunged in recent weeks.

But Lopez Obrador, 65, has an undeniably strong mandate: he won a landslide victory in the July 1 elections, together with large majorities in both houses of Congress for his coalition -- led by the party he founded just four years ago, Morena.

It was the biggest win for any president, and the first for a leftist, since Mexico transitioned to multi-party democracy in 2000.

Lopez Obrador traveled to his swearing-in ceremony in his small white Volkswagen Jetta, making his way through a sea of supporters.

Jose Angel Mejia, 38, was in the crowd outside the lower house to fete the new president.

"It's a historic day, I still can't believe it," he said, raising his eight-year-old son's arm in the air in celebration. We're going to have a change at last."