Police were searching Thursday for the outspoken mayor of Seoul, long seen as a potential South Korean presidential candidate, after he was reported missing by his daughter.
A police complaint -- allegedly involving sexual assault -- was filed against Park Won-soon by a former Seoul City employee on Wednesday and local media said a television channel had been due to broadcast a programme on the previously unreported case on Thursday evening.
Park's daughter reported him missing on Thursday afternoon, saying her father had been unreachable for several hours, police said.
He left his house after saying what sounded like "last words" and his phone had been turned off, she told police.
A heavyweight figure in the ruling centre-left Democratic party, Park has run South Korea's sprawling capital -- home to almost a fifth of the national population -- for nearly a decade.
He has consistently been talked of as a potential candidate in the race to succeed current President Moon Jae-in, and did not deny ambitions on that front when asked by AFP earlier this year.