BRASILIA, Jan 1 (AFP) - Luiz Inacio Lula da Silva was sworn in as Brazil's president on Sunday, delivering a searing indictment of far-right former leader Jair Bolsonaro and vowing a drastic change of course to rescue a nation plagued by hunger, poverty and racism.

In a speech to Congress after officially taking the reins of Latin America's biggest country, the leftist said democracy was the true winner of the October presidential vote, when he ousted Bolsonaro in the most fraught election for a generation.

Bolsonaro, who left Brazil for the United States on Friday after refusing to concede defeat, rattled the cages of Brazil's young democracy with baseless claims of electoral weaknesses that birthed a violent movement of election deniers.

"Democracy was the great victor in this election, overcoming ... the most violent threats to freedom to vote, and the most abject campaign of lies and hate plotted to manipulate and embarrass the electorate," Lula told lawmakers.

Lula, who was behind bars during Bolsonaro's 2019 inauguration on graft convictions that were later overturned, delivered a veiled threat to his predecessor.

"We do not carry any spirit of revenge against those who tried to subjugate the nation to their personal and ideological designs, but we will guarantee the rule of law," Lula said, without mentioning Bolsonaro by name. "Those who erred will answer for their errors."

He also accused Bolsonaro's administration of committing "genocide" by failing to respond properly to the COVID-19 virus that killed more than 680,000 Brazilians.

"The responsibilities for this genocide must be investigated and must not go unpunished," he said.

Although Bolsonaro's Florida trip insulates him from any immediate legal jeopardy in Brazil, he now faces mounting judicial risks - related to his anti-democratic rhetoric and his pandemic handling - after losing his presidential immunity, legal experts said.

Lula's plans for government provided a stark contrast to Bolsonaro's four years in office, which were characterized by backsliding on environmental protections in the Amazon rainforest, looser gun laws and weaker protections for indigenous peoples and minorities.

Lula said he wants to turn Brazil, one of the world's top food producers, into a green superpower.