Mainstream historians say up to 200,000 women, mostly from Korea but also other parts of Asia including China, were forced to work in Japanese military brothels during World War II.
The plight of the "comfort women" is a hugely emotional issue that has marred ties between the two Asian neighbours for decades. For many South Koreans it epitomises the abuses committed under Japanese rule.
Activists have in recent years set up dozens of statues -- typically a young, barefoot girl wearing a traditional hanbok outfit with her hands on her knees -- in public venues as a symbol of the victims.
But the city bus company said it wanted to install statues on five buses running through downtown Seoul to keep the women's memory alive.
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"It is designed to remind South Koreans of suffering the women went through," said Rim Jin-Wook, the head of Dong-A Traffic Service that organised the event.
The buses, whenever they pass by the Japanese embassy in central Seoul, play brief explanations about the wartime sex slaves over their audio systems.
"It's so heartbreaking to see this girl statue partly because she looks about my age," Jennifer Lee, a 19-year-old college student, told AFP.
"It horrifies me just to imagine what these women went through."
Last month, the new South Korean government under President Moon Jae-In launched a task force to investigate potential problems in the deal with Tokyo concerning the comfort women.
Activists are now pushing for Seoul to designate August 14 -- a day before the anniversary of the country's independence -- as a state memorial day for former comfort women.