Flags at San Francisco’s City Hall flew at half staff on Tuesday as the city mourned the sudden death of Ed Lee, its first Chinese-American mayor.

Lee, 65, died at 1:11 am on Tuesdayat Zuckerberg San Francisco General Hospital, according to his office.Local news accounts said he had suffered a heart attack while grocery shopping, but his office did not immediately give a cause of death.

Lee was in critical condition when he arrived at the hospital by ambulance shortly after 10 p.m. on Monday, according to Dr Susan P. Ehrlich, the hospital’s chief executive. “We attempted life-saving measures for several hours. We expect the medical examiner to determine the cause of death.”Lee’s family asked that further medical details not be released, she said.

He was surrounded by his family, including his wife Anita and his two daughters, Brianna and Tania, as well as many political leaders when he died, according to Lee’s office.

In accordance with the City Charter, Board of Supervisors President London Breed became acting mayor of the city of more than 850,000 people. She is a native San Franciscan who was raised by her grandmother in a housing project. Breedis San Francisco’s first female black mayor.

Condolences from around the nation and beyond commemorated Lee for his contributions to advance San Francisco as the world’s hub for innovation and technology, and his continuous efforts advocating for the city’s low-income and underserved populations.

He became San Francisco’s 43rd mayor in 2011 and was re-elected in 2015. The son of immigrants from China, his election was a milestone for Chinese Americans, many of whose ancestors came from China to America as laborers in the 1800s and were mistreated and suffered decades of discrimination, including the Chinese Exclusion Act of 1882 which stopped Chinese immigration for nearly a century. It was repealed on December 17, 1943.

"Mayor Lee served San Francisco and all San Franciscans most of his life and he won the admiration of all. He was the symbol and model for Asian Americans who aspire to public services in this country," said Committee of 100 Northern California Regional Chair Ken Fong.

“My hometown is Taishan in Guangdong. I can speak Taishan dialect,” Leehad said in an interview with China Daily. “I visited my hometown often.”

As mayor, he led many business and trade delegations to China to facilitate collaborations in fields of high-tech, smart city and environmental protection. His most recent trip to China was in October when Lee visited Shanghai, a longtime sister city of San Francisco.

The Chinese Consulate General in San Francisco said in a statement, “As the first Chinese-American Mayor of San Francisco, Mayor Ed Lee made tremendous contributions to friendly exchanges and mutually beneficial cooperation between San Francisco and China. He will be remembered as a great mayor and an advocate and practitioner of US-China friendship.”

Lee "will forever be remembered as a human rights hero in the hearts of San Franciscans,” said a statement issued by the Comfort Women Justice Coalition (CWJC), a diverse coalition of community-based groups and individuals established in August 2015. Its mission is to memorialize “Comfort Women” in San Francisco and to educate the public about Japanese military sexual slavery and human trafficking system during World War II.

“Mayor Ed Lee was a man with a big heart. He stood for those who didn't have the voice to speak for themselves. He met with our beloved Grandma Yongsoo Lee, the survivor of the Japanese military sexual slavery, where he shared compassion, friendship and laughter with her,” the statement said.

Recently, Lee signed the City Resolution to make the "Comfort Women Column of Strength", a monument CWJC has dedicated to erecting at the St. Mary’s Square Annex on September 22 to remember victims of World War II “Comfort Women”, the City's own "Comfort Women" Memorial. Lee did so despite the threat from his counterpart in Osaka, Japan, of ending the 60-year-old sister city relationship with San Francisco.

Lee presided over one of the most explosive periods of growth in the city’s history. He brought employers back to the city, and played an instrumental role in attracting tech companies to San Francisco and convincing them to stay.

US House Minority Leader Nancy Pelosi, who represents San Francisco in Congress, praised Lee as "a true gentleman of great warmth, positivity and kindness."

"I don’t know San Francisco without Ed Lee,” former mayor Willie Brown said. Lee served as head of purchasing during Brown’s tenure as mayorfrom 1996 to early 2004.

US Senator Dianne Feinstein, who became mayor of the city following the assassination of Mayor George Moscone in 1978, called it a “very sad day” for the city and for all those who knew Lee.

US Senator Kamala Harris, who served as San Francisco district attorney said that Lee’s was a fierce advocate for civil rights and worked tirelessly for workers’ rights "and his leadership will be missed.’’

Governor Jerry Brown called Lee “a true champion for working people.”

Lieutenant Governor Gavin Newsom, a former San Francisco mayor who appointed Lee as his replacement in 2011 when he resigned to become California’s lieutenant governor in January 2011, said that “San Francisco has lost a selfless leader, a dedicated servant to the public, and a tireless bearer of equality’s torch.”

Edwin Mah Lee was born to parents who came to the United States from the Chinese province of Guangdong and settled in Seattle. He was the fifth of six children. His father worked in local restaurants and his mother did odd jobs around Seattle. When he was 15, Lee’s father died of a heart attack, and Lee worked in restaurants to help support his family.

He graduated from Bowdoin College in Maine in 1974 and earned a law degree at the University of California at Berkeley, where he also became interested in politics.

At his first swearing-in, in 2011, he commented on his rise from being a housing advocate to virtually unknown civil servant to city leader.“Decades ago, I was about as anti-establishment as one could be,” he said. “But today, like you, I’m trying to make the establishment work for all San Franciscans.”

Lee was passionate about immigrant rights. In January, he insisted that San Francisco would remain a sanctuary city “now, tomorrow, forever.”

In an interview with The New York Times last year, Lee said he had been drawn to San Francisco for its diversity and tolerance. "The main attraction was a kind of feeling that freedom of expression and maybe a person of a different ethnic background could be welcomed and succeed,” he said.