Watch: South Koreans march with coffin of Kim Bok-dong in 'comfort women' protest

South Korean protesters marched alongside the coffin of a 'comfort women' campaigner to the Japanese embassy on Friday in a protest over Japan's use of forced labour in its wartime brothels.

A hearse carried the casket of Kim Bok-dong, who died this week at 93, to the embassy to highlight the plight of "comfort women," a Japanese euphemism for women who were forced into prostitution and sexually abused at Japanese military brothels before and during World War-II.

"Japan must apologise," some of the protesters chanted during the march. "Japan provide formal compensation."

Mourners carried banners thanking Kim for her devotion to the cause and called on Japan to atone for its actions. Some signs were in the shape of butterflies, a symbol of freedom for suffering women.

The "comfort women" are a contentious issue between the two Asian neighbours which share a bitter history stemming from Japan's 1910-45 colonisation of the Korean peninsula.

Japan says the claims have been settled by past agreements and apologies, and that the continued dispute may threaten relations between the two countries.

Deputy Chief Cabinet Secretary Yasutoshi Nishimura told reporters in Tokyo on Friday that it would be a problem if the event caused a "public disturbance" at the embassy or "infringement on its dignity."

Kim, who died in hospital after battling cancer, was one of the first victims to come forward in 1992 and became a fixture at weekly protests outside the Japanese embassy.

Kim said she was 14 when first sent to a military brothel, and forced to provide sex for Japanese soldiers also in China, Hong Kong, Indonesia, Malaysia and Singapore for eight years.

Never married, she dedicated her life to advocacy and travelled the world to tell her story.

"I first met her during a protest in 2012 and she was sitting up straight even in the rain as she spoke about her struggle," said Kim Sam, a 27-year-old student campaigner.

"Upright, dignified - that's how she always was, first as a victim and later as a human rights activist. She's a role model I respect the most."

Lee Yong-soo, a fellow victim who paid her respects despite the cold weather, laid flowers at a bronze statue of a girl erected near the Japanese embassy to represent the women.

Many mourners quietly sobbed and wiped their eyes as organisers aired a video clip in which Kim shouted during a rally that she would raise similar girl statues around the world until Tokyo sincerely apologised.

Kim was a vocal critic of a 2015 deal in which Tokyo apologised to the victims and provided 1 billion yen ($9.2 million) to a fund in Seoul to help them.

She said the apology was not sincere because some Japanese leaders continued to deny the women were forced to work in brothels.

Moon's government has said it will not seek to renegotiate the 2015 deal. Last year it vowed to shut down the Japan-sponsored fund and pursue a more "victim-oriented" approach.

With Kim's death, only 23 registered South Korean survivors are still alive, underscoring a sense of urgency behind efforts by the women to receive a formal apology and legal compensation from Japan while their voices can still be heard.