Veteran leftist politician Andres Manuel Lopez Obrador was sworn in as Mexican president on Saturday, promising a radical change of regime in a country struggling with gang violence, chronic poverty and corruption.

Backed by a giant Mexican flag, the 65-year-old took the oath of office in Mexico's lower house of Congress, saying his

administration would overturn what he called the disastrous legacy of decades of "neo-liberal" governments.

"Starting now, transformation is underway, ordered and peaceful, but at the same time radical, because we will end the corruption and impunity that impede Mexico's rebirth," he said.

The first leftist to take office in Mexico in a generation also tried to reassure business after markets crashed since the July 1 election on worries about his policies, including the abrupt cancellation of a $13-billion US airport project.

More than 25,000 murders in year

Lopez Obrador reiterated that investments in the country of 130 million people would be safe, and vowed to respect central bank independence.

Saying his government would make savings by stopping losses from the public purse into the "sewer of corruption," he promised not to raise national debt or taxes.

But in a reference to one of his heroes, the former president Benito Juarez who separated the church and the state in Mexico, Lopez Obrador promised his government would ensure a divide between economic and political power in the country.

Lopez Obrador, left, appears with then-president Enrique Pena Nieto at the National Palace in Mexico City during a ceremony where the newly elected leftist leader presented his new cabinet, on August 20. (Alfredo Estrella/AFP/Getty Images)

He said the government of his predecessor Enrique Pena Nieto had caused a plunge in oil output by opening the energy industry in Latin America's second-largest economy to private investment.

Some of the toughest problems Lopez Obrador faces are more severe than when Pena Nieto took office in 2012, vowing to tackle unprecedented violence. Like his predecessor, the new president says security will be his top priority.

More than 25,000 murders, a record, were logged in 2017. But over 10,000 were registered between July and October, the bloodiest four-month period since modern records began in 1997.

Arrived at Congress in white VW sedan

Reflecting his austere manner, Lopez Obrador arrived at Congress in a modest white Volkswagen sedan with little visible security, in contrast to the opulent lifestyles of his predecessors.

In another sign of change, the doors of Pena Nieto's official Los Pinos residence were thrown open to public visitors on Saturday. Lopez Obrador has said he will save money by living in an apartment in the presidential palace.

Pena Nieto returned to Mexico from a G20 summit in Argentina on Saturday morning, on the last official flight for his Boeing Dreamliner presidential plane, which Lopez Obrador is putting up for sale.