SAN FRANCISCO — San Francisco welcomed its first Asian-American leader Tuesday, as City Administrator Edwin Lee was sworn in as interim mayor before a crowd of hundreds.

The Board of Supervisors voted unanimously to appoint Lee to fill the remainder of Mayor Gavin Newsom’s term. Newsom was sworn in Monday as California’s lieutenant governor.

Immediately following the vote, Lee took the oath of office before a packed audience of family members, current and former city leaders and supporters from the Chinese-American community who gathered in the City Hall rotunda.

"This is a big step we’re making as a city," said Supervisor Eric Mar, one of four Asian-Americans serving on the 11-member board.

San Francisco’s population of 815,000 is nearly one-third Asian — the largest percentage of any county in the continental United States, according to U.S. Census Bureau.

With Lee serving as the city’s 43rd mayor, San Francisco is now the largest in the country with an Asian-American leader, said Don Nakanishi, director emeritus of the UCLA Asian Studies Center.

Earlier this month, neighboring Oakland inaugurated Mayor Jean Quan, the first Asian-American woman to helm a major U.S. city. Quan, a longtime acquaintance of Lee’s, also was present at Tuesday’s ceremony to show her support.

The 58-year-old will serve as interim mayor until next January, when the winner of November’s mayoral election will take over. Lee, a city employee for more than 20 years, has said he does not plan to run.

But he said Tuesday he sees the temporary job as a "tremendous, historic opportunity."

"I will work with each and every one of you to see that constituents are well-served, that the doors of diversity and opportunity are open," he told the supervisors.

Newsom on Tuesday voiced his strong support for his successor.

"I have all the confidence in the world in Mayor Lee’s ability to lead the city we both love," he said.

The former mayor delayed his transition to Sacramento until after four new supervisors took office on Saturday, in an effort to ensure that Lee would replace him. Several members of the previous board originally backed other interim-mayor nominees, though all but one had moved to Lee’s corner by late last week.

Lee worked as a private sector attorney for 10 years before beginning his public service career in 1989, when former Mayor Art Agnos named him investigator under the city’s first whistleblower ordinance. He has since worked under four mayors, heading the Human Rights Commission and the Department of Public Works and overseeing purchasing for the city.

He took over as city administrator in 2005.

That record makes Lee a solid choice to lead a city grappling with a $379 million deficit, his supporters said.

"This is not a time for someone who needs a learning curve," said Supervisor Scott Wiener. "You need someone who can step in on day one, and Ed Lee will do that."