New York's new Mayor Bill de Blasio was sworn in Wednesday promising to restore progressive ideals and end growing economic inequality in America's biggest city.

De Blasio, who in November won a landslide election to become New York's first Democratic mayor in 20 years, took the oath of office on the steps of City Hall, with former US president Bill Clinton presiding.

"We are called to put an end to economic and social inequalities that threaten to unravel the city we love," de Blasio said after taking the oath as its 109th mayor on a frigid afternoon.

"So today, we commit to a new progressive direction in New York."

As the city's new leader and top Democrat, de Blasio said he would seek reforms so the city would be recognized "not as the exclusive domain of the one percent, but a place where everyday people can afford to live, work and raise a family."

He also set forth a progressive agenda that included expanding a paid sick-leave law, providing more affordable housing, reforming New York's controversial stop-and-frisk policy, and guaranteeing full-day universal pre-kindergarten schooling for every child in the city and after-school programs for middle schoolers.

A tax increase on those earning more than $500,000 is due to fund the school initiatives.

Clinton, who introduced the mayor, said he strongly endorsed de Blasio's "core campaign commitment that we have to have a city of shared opportunities, shared prosperity, shared responsibilities."

De Blasio worked in the Clinton administration during his days in the Department of Housing and Urban Development.

Also attending the ceremony was the ex-president's wife, Hillary Clinton, tipped by politicos as a 2016 presidential favorite, and whose successful 2000 Senate campaign de Blasio managed.

The new mayor was sworn in using a Bible that once belonged to former US president Franklin D. Roosevelt, the architect of America's New Deal reforms that provided a safety net for Americans suffering during the Great Depression.

The flashy ceremony followed a more intimate first swearing-in one minute after midnight in front of de Blasio's Brooklyn home, where he was flanked by his wife Chirlane and their two teenaged children.

"This is the beginning of a road we will travel together," he told a few dozen supporters gathered there, during a short speech.

End of Bloomberg's 12-year era

The modest midnight oath was in stark contrast with that taken by his predecessor, Michael Bloomberg, in 2002 when he took the oath of office in Times Square amid confetti and a massive swarm of revelers.

More than a decade later, the brash billionaire concluded his 12-year reign Tuesday, ending an era that heralded major changes for America's largest city, but that also deepened the schism between rich and poor.

De Blasio, a former member of New York's City Council towering at six feet, five inches (1.96 meters), emphasized his desire to establish a progressive administration.

It was a message echoed throughout his campaign, when the high visibility of his African-American wife and biracial children helped the public advocate connected to middle-class families and the city's diverse electorate.

The new mayor was swept into office on November 5 with an impressive 73 percent vote, a testament to New Yorkers' desire for change after 12 years under Bloomberg.

During Bloomberg's three terms, the city became safer, greener and healthier, but critics were quick to peg the finance-sector billionaire as a politician for the wealthy in a city with the country's largest inequality gap.

New York counts nearly 400,000 millionaires and 3,000 multi-millionaires among its ranks, while 21.2 percent of the population lives below the poverty line.

The city's newest leader has created high hopes among its Hispanic and black populations, which respectively account for 28.6 percent and 25.5 percent of New York's 8.3 million inhabitants.

De Blasio made a brief Spanish statement during his swearing-in ceremony.