Police officers said they are looking for Mayor Park Won-sun at Seoul's Sungbuk neighborhood where his mobile phone signal was last detected.
His daughter called police earlier Thursday and said her father has been unaccounted for, the police officers said, requesting anonymity because they were not authorized to speak to media on the matter.
Kim Ji-hyeong, an official from the Seoul Metropolitan Government, confirmed that Park did not show up for work on Thursday because of unspecified reasons and canceled all his schedules, including a meeting with a presidential official at his Seoul City Hall office.
A longtime civic activist and human rights lawyer, Park was elected Seoul mayor in 2011 and voted into his third and last term in June last year.
A member of President Moon Jae-in’s liberal Democratic Party, Park had been considered a potential presidential hopeful for the liberals in the 2022 elections.