San Francisco Mayor Edwin M. Lee died early Tuesday morning at Zuckerberg San Francisco General Hospital, according to a statement from his office.
Lee, 65, had been mayor since 2011.
Board of Supervisors President London Breed became Acting Mayor of San Francisco, effective immediately, the mayor's office said in the statement. Breed will appear at a press availability Tuesday morning at City Hall.
Details have not been made available regarding the circumstances of Lee's death.
"Our thoughts and prayers are with his wife Anita, his two daughters, Brianna and Tania, and his family," the mayor's office said in a statement.